Author Topic: Forum Timestamps Inconsistent with Other Accounts of Events  (Read 8860 times)

Offline ThreadSnake

I have been looking through posts on this board, and I've noticed some strange occurrences where the timestamps of posts do not line up particularly well with local times from live streams, and timestamps on other websites linked.

for some examples, the first time I noticed this was when I was gathering information on Starhopper's first tests in the SpaceX BFS - Phase 1 - StarHopper - Photos and Updates thread:

One example:

https://forum.nasaspaceflight.com/index.php?topic=47120.msg1927104#msg1927104

On LabPadre's stream, the suspected preburner fire was at 16:14:48CDT (UTC -5), or 21:14:48UTC.
But the forum post was at 20:19:10UTC, with an edit at 20:27:31UTC according to the forum, almost 50 minutes before the actual test occurs according to the stream.

Another example:

https://forum.nasaspaceflight.com/index.php?topic=47120.msg1925576#msg1925576
and
https://forum.nasaspaceflight.com/index.php?topic=47120.msg1925580#msg1925580

The tweet's timestamp was 2019-03-21T20:38:00.000Z, which is means 20:38:00 Zulu, or UTC.
The forum posts, however, were last edited at 19:45:26UTC and 19:52:05UTC, 46 minutes before the tweet was posted.

It looks as if some time stamps on this forum are an hour early from the rest; maybe it is getting confused with various daylight savings time standards? Such as in the southern hemisphere, they practice daylight savings in their summer, which is opposite from north's summer.

Before anyone asks, I have my time offset in my profile settings to 0, and this also matches my computer's UTC clock as well.

I made a post on the data collection thread I made explaining some of this 2 days ago, but haven't got responses there.
https://forum.nasaspaceflight.com/index.php?topic=51485.msg2109127#msg2109127
So that is why I made a thread to discuss why this is happening.

I think some information can be taken from this discussion I found on the subject of Simple Machine Forum timestamps:
https://groups.google.com/forum/#!topic/bit.listserv.ibm-main/_ogPJ2dMBQU
and specifically, this one highlights that there is some confusion with what local times use daylight savings or not:
https://groups.google.com/d/msg/bit.listserv.ibm-main/_ogPJ2dMBQU/hF7Uqw9LvOIJ
I have a hunch that this might have something to do with it, but it could be something completely different.

Let me know if you guys have any new explanations or already existing explanations I don't know about for what exactly is happening/happened with this problem.
Hello, I gather and organize Starship development data.
[email protected]:01 UTC - Timeline Updates, [email protected]:01 UTC: RGV pic parts census.

Offline billh

  • Full Member
  • ****
  • Posts: 717
  • Houston
  • Liked: 917
  • Likes Given: 618
Probably time zone differences.

Offline intelati

Probably time zone differences.

And a ten minute delay is reasonable. (an hour difference-50 minute error)
Starships are meant to fly

Offline ChrisWilson68

  • Senior Member
  • *****
  • Posts: 5266
  • Sunnyvale, CA
  • Liked: 4987
  • Likes Given: 6458
But the forum post was at 20:19:10UTC, with an edit at 20:27:31UTC according to the forum

Before anyone asks, I have my time offset in my profile settings to 0, and this also matches my computer's UTC clock as well.

This site doesn't give you timestamps in UTC.  It gives them in your local time.  Just because you set the current offset from UTC to zero doesn't mean it is giving you UTC for past posts.  It probably assumes you're in a time zone that observes daylight savings time that just happens to currently have a zero offset from UTC but a one-hour offset from UTC at other times of year.

The forum only lets you specify the current offset from UTC.  It doesn't let you set something like an Olsen name that would include daylight savings information.  But I've noticed that I don't have to change anything when the daylight savings change happens in my location, the forum just adjusts my offset automatically.

I don't know how it's deciding the daylight savings time rules for your account, but I think it is deciding them for you.  Maybe it gets it from your browser.  Maybe it uses your IP address to infer a location.  Maybe it just assumes based on your UTC offset.  I don't know.  But I think the evidence suggests the timestamps it's giving you include daylight savings.

Offline starskale

  • Full Member
  • *
  • Posts: 179
  • Liked: 222
  • Likes Given: 167
I've confirmed the issue here. The posts in question are during daylight savings observation and my timezone is currently observing daylight savings. The post with the tweet is the easiest way to see the issue.

I can see that this post matches the time on my computer's clock (PDT) and so all posts should be correctly displaying in PDT (UTC-7). Adding 7hr to the post times shown gives a time that is too early by an hour.
« Last Edit: 07/22/2020 06:31 pm by starskale »

Offline ThreadSnake

But the forum post was at 20:19:10UTC, with an edit at 20:27:31UTC according to the forum

Before anyone asks, I have my time offset in my profile settings to 0, and this also matches my computer's UTC clock as well.

This site doesn't give you timestamps in UTC.  It gives them in your local time.  Just because you set the current offset from UTC to zero doesn't mean it is giving you UTC for past posts.  It probably assumes you're in a time zone that observes daylight savings time that just happens to currently have a zero offset from UTC but a one-hour offset from UTC at other times of year.

The forum only lets you specify the current offset from UTC.  It doesn't let you set something like an Olsen name that would include daylight savings information.  But I've noticed that I don't have to change anything when the daylight savings change happens in my location, the forum just adjusts my offset automatically.

I don't know how it's deciding the daylight savings time rules for your account, but I think it is deciding them for you.  Maybe it gets it from your browser.  Maybe it uses your IP address to infer a location.  Maybe it just assumes based on your UTC offset.  I don't know.  But I think the evidence suggests the timestamps it's giving you include daylight savings.

If it was inferring that I am in daylight savings time, wouldn't displayed times be one hour ahead?
(I am in the northern hemisphere in the US observing local time EDT at the moment)
I'd suggest people that see this to check if they have the same predicament on their own devices. The method I used to get the twitter timestamp is with the inspect element tool on the date in the tweet.
If we know that we can reproduce the problem, we can have a better idea of what's happening.

As a sidenote publically, there are several things that could be going on here, so try to approach it with an open mind.
Hello, I gather and organize Starship development data.
[email protected]:01 UTC - Timeline Updates, [email protected]:01 UTC: RGV pic parts census.

Offline ChrisWilson68

  • Senior Member
  • *****
  • Posts: 5266
  • Sunnyvale, CA
  • Liked: 4987
  • Likes Given: 6458
If it was inferring that I am in daylight savings time, wouldn't displayed times be one hour ahead?
(I am in the northern hemisphere in the US observing local time EDT at the moment)

If it thinks you are currently observing daylight savings and it thinks your current offset from UTC is 0 hours, then it believes that during non-daylight-savings times of year you are one hour behind daylight savings.  So when showing you a timestamp that is noon UTC it would tell you it's 11:00am in your local time.  If you interpret that 11:00am as being UTC, the timestamps would seem to you to be 1 hour before the times they actually represent.

Offline JonathanD

  • Full Member
  • ****
  • Posts: 619
  • Liked: 848
  • Likes Given: 255
Yet one more reason to kill Daylight Savings!

Offline ThreadSnake

If it was inferring that I am in daylight savings time, wouldn't displayed times be one hour ahead?
(I am in the northern hemisphere in the US observing local time EDT at the moment)

If it thinks you are currently observing daylight savings and it thinks your current offset from UTC is 0 hours, then it believes that during non-daylight-savings times of year you are one hour behind daylight savings.  So when showing you a timestamp that is noon UTC it would tell you it's 11:00am in your local time.  If you interpret that 11:00am as being UTC, the timestamps would seem to you to be 1 hour before the times they actually represent.

That is a good theory, but the problem in this situation is that the posts in question are also posted in times of the year where daylight savings time exists in the US.
Hello, I gather and organize Starship development data.
[email protected]:01 UTC - Timeline Updates, [email protected]:01 UTC: RGV pic parts census.

Offline DigitalMan

  • Full Member
  • ****
  • Posts: 1546
  • Liked: 1067
  • Likes Given: 74
If it was inferring that I am in daylight savings time, wouldn't displayed times be one hour ahead?
(I am in the northern hemisphere in the US observing local time EDT at the moment)

If it thinks you are currently observing daylight savings and it thinks your current offset from UTC is 0 hours, then it believes that during non-daylight-savings times of year you are one hour behind daylight savings.  So when showing you a timestamp that is noon UTC it would tell you it's 11:00am in your local time.  If you interpret that 11:00am as being UTC, the timestamps would seem to you to be 1 hour before the times they actually represent.

That is a good theory, but the problem in this situation is that the posts in question are also posted in times of the year where daylight savings time exists in the US.

Have you looked at your own posts and noticed a time difference?

Offline ChrisWilson68

  • Senior Member
  • *****
  • Posts: 5266
  • Sunnyvale, CA
  • Liked: 4987
  • Likes Given: 6458
Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #10 on: 07/22/2020 07:17 pm »
If it was inferring that I am in daylight savings time, wouldn't displayed times be one hour ahead?
(I am in the northern hemisphere in the US observing local time EDT at the moment)

If it thinks you are currently observing daylight savings and it thinks your current offset from UTC is 0 hours, then it believes that during non-daylight-savings times of year you are one hour behind daylight savings.  So when showing you a timestamp that is noon UTC it would tell you it's 11:00am in your local time.  If you interpret that 11:00am as being UTC, the timestamps would seem to you to be 1 hour before the times they actually represent.

The two examples in your original post are from dates in March that are after daylight savings starts in the US but before it starts in the UK and other parts of Europe.  Since you told it your offset from UTC is zero, it could well be assuming you're in a European time zone where you are currently in UTC because of daylight savings but in mid-March you were one hour behind UTC because you weren't in daylight savings then.

Offline ThreadSnake

Quote
I think you could be on to something. I will try changing my offset to -6 and see if it changes the relative difference.

No, it did not solve the problem by changing the time to Boca Chica's local time

Either the forum is inferencing time zones from something else, or it inferencing time zones isn't the problem
« Last Edit: 07/22/2020 07:31 pm by ThreadSnake »
Hello, I gather and organize Starship development data.
[email protected]:01 UTC - Timeline Updates, [email protected]:01 UTC: RGV pic parts census.

Offline ThreadSnake

I'm pretty sure that the Twitter timestamp is most likely to be accurate of the sources, so by extension, this forum is the most likely to be 1 hour early for whatever reason.
Hello, I gather and organize Starship development data.
[email protected]:01 UTC - Timeline Updates, [email protected]:01 UTC: RGV pic parts census.

Offline starskale

  • Full Member
  • *
  • Posts: 179
  • Liked: 222
  • Likes Given: 167
Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #13 on: 07/22/2020 08:17 pm »
If it was inferring that I am in daylight savings time, wouldn't displayed times be one hour ahead?
(I am in the northern hemisphere in the US observing local time EDT at the moment)

If it thinks you are currently observing daylight savings and it thinks your current offset from UTC is 0 hours, then it believes that during non-daylight-savings times of year you are one hour behind daylight savings.  So when showing you a timestamp that is noon UTC it would tell you it's 11:00am in your local time.  If you interpret that 11:00am as being UTC, the timestamps would seem to you to be 1 hour before the times they actually represent.

The two examples in your original post are from dates in March that are after daylight savings starts in the US but before it starts in the UK and other parts of Europe.  Since you told it your offset from UTC is zero, it could well be assuming you're in a European time zone where you are currently in UTC because of daylight savings but in mid-March you were one hour behind UTC because you weren't in daylight savings then.

I live in PDT and can confirm the same issue exists. And yes, I can confirm the timestamps of my posts match the correct time.

Offline TomH

  • Senior Member
  • *****
  • Posts: 2685
  • Vancouver, WA
  • Liked: 1533
  • Likes Given: 709
Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #14 on: 07/23/2020 06:20 am »
One semantic nit: It is Daylight Saving Time, not Daylight Savings Time. In this context saving serves as a verbal adjective, while savings is a verbally derived noun, e.g. savings is what you have in the bank.

Think of it this way, is the Heimlich a life savings maneuver or a life saving maneuver?
« Last Edit: 07/23/2020 06:22 am by TomH »

Offline ChrisWilson68

  • Senior Member
  • *****
  • Posts: 5266
  • Sunnyvale, CA
  • Liked: 4987
  • Likes Given: 6458
Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #15 on: 07/23/2020 01:18 pm »
One semantic nit: It is Daylight Saving Time, not Daylight Savings Time. In this context saving serves as a verbal adjective, while savings is a verbally derived noun, e.g. savings is what you have in the bank.

Think of it this way, is the Heimlich a life savings maneuver or a life saving maneuver?

It's not as simple as that.

Here's what the Oxford Dictionary of American Usage and Style has to say on the subject, as quoted by Wikipedia:

Quote
Although the singular form daylight saving time is the original one, dating from the early 20th century—and is preferred by some usage critics—the plural form is now extremely common in AmE. [...] The rise of daylight savings time appears to have resulted from the avoidance of a miscue: when saving is used, readers might puzzle momentarily over whether saving is a gerund (the saving of daylight) or a participle (the time for saving). [...] Using savings as the adjective—as in savings account or savings bond—makes perfect sense. More than that, it ought to be accepted as the better form.

https://en.wikipedia.org/wiki/Daylight_saving_time

Note that while the official title of the Wikipedia article uses "saving", the very first sentence of the article says it is also called "daylight savings time".

Offline ThreadSnake

I want to gather more information on what posts/times of the year this occurs, to get a larger dataset to analyze. I will make some more posts on here once I have that information, but for now, I will be using any other sources I can find linked to the events I'm researching.
Hello, I gather and organize Starship development data.
[email protected]:01 UTC - Timeline Updates, [email protected]:01 UTC: RGV pic parts census.

Offline launchwatcher

  • Full Member
  • ****
  • Posts: 704
  • Liked: 627
  • Likes Given: 891
Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #17 on: 07/23/2020 07:59 pm »
I want to gather more information on what posts/times of the year this occurs, to get a larger dataset to analyze. I will make some more posts on here once I have that information, but for now, I will be using any other sources I can find linked to the events I'm researching.
Rather than treating this as a black box problem, you could look at the code underlying the forum (like I just did).

Download one of the source archives from: https://download.simplemachines.org/index.php?archive;b=4;v=99

Inside, find the definitions of the underlying database schema.   Observe that it uses an integer to store post timestamps.

Post timestamps are stored in a database as a POSIX timestamp (seconds since 1970-01-01 00:00 UTC, not counting leap seconds).

Conversions are done by the PHP code in .../Sources/Subs.php.

But then observe how it adjusts the integer timestamp with both a user and forum offset in hours prior to feeding the timestamp into strftime().   strftime() then does its own DST adjustments based on a complex set of location-dependent rules managed by the standard UNIX timezone package.   There's a bit of garbage in, garbage out going on here -- you're going to see some possibly errnoneous adjustments, especially for events occurring near DST adjustments.

my recommendation would be to set your timezone offset in your forum profile to 0 for any timestamp analysis and hope that the server is actually running in UTC rather than in TZ=Europe/London.


Online tacoLover7916

  • Member
  • Posts: 18
  • USA
  • Liked: 22
  • Likes Given: 84
Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #18 on: 07/23/2020 08:08 pm »
If it was inferring that I am in daylight savings time, wouldn't displayed times be one hour ahead?
(I am in the northern hemisphere in the US observing local time EDT at the moment)

If it thinks you are currently observing daylight savings and it thinks your current offset from UTC is 0 hours, then it believes that during non-daylight-savings times of year you are one hour behind daylight savings.  So when showing you a timestamp that is noon UTC it would tell you it's 11:00am in your local time.  If you interpret that 11:00am as being UTC, the timestamps would seem to you to be 1 hour before the times they actually represent.

The two examples in your original post are from dates in March that are after daylight savings starts in the US but before it starts in the UK and other parts of Europe.  Since you told it your offset from UTC is zero, it could well be assuming you're in a European time zone where you are currently in UTC because of daylight savings but in mid-March you were one hour behind UTC because you weren't in daylight savings then.


ChrisWilson68 makes a good point. The referenced posts are in the window between the USA and Europe change for DST. I don't think it has anything to do with the user's preferred UTC offset. I think it has to do with when the site changes it's time to DST. By the looks of things it uses a later date that the US to change to DST.

My bet is that the site has a single time that it does the time change from standard to DST. Perhaps the site uses the last Sunday of March as many European countries do. Since Boca Chica changed its time on the second Sunday of March as the US does, leaping ahead one hour, this would make sense of the discrepancy. In Boca Chica the time was an hour ahead because it had changed to DST already but the site hadn't realized the change.

The website was just waiting another week or two to adjust the time forward and thus Boca Chica appeared to be one hour in the past.

Offline launchwatcher

  • Full Member
  • ****
  • Posts: 704
  • Liked: 627
  • Likes Given: 891
Re: Forum Timestamps Inconsistent with Other Accounts of Events
« Reply #19 on: 07/23/2020 08:59 pm »
My bet is that the site has a single time that it does the time change from standard to DST. Perhaps the site uses the last Sunday of March as many European countries do. Since Boca Chica changed its time on the second Sunday of March as the US does, leaping ahead one hour, this would make sense of the discrepancy. In Boca Chica the time was an hour ahead because it had changed to DST already but the site hadn't realized the change.
That's consistent with a quick look at the underlying forum code -- it uses the system's default DST transition rules and then adds in your offset from GMT, rather than trying to use a client-dependent, client-supplied set of rules for DST transition.

What's odd is that if I add "%Z" (timezone name) and "%s" (UNIX/POSIX timestamp in decimal) to the Time Format string in the Profile, it displays "BST" as a timezone but displays times consistent with UTC/GMT:
Current forum time: 2020-07-23, 20:55:27 (BST: 1595537727)

while on my end if I ask for London time I get:
TZ=Europe/London date +"%Y-%m-%d, %H:%M:%S (%Z: %s)"
2020-07-23, 21:56:55 (BST: 1595537815)

which is British Summer Time (UTC+1)



Tags:
 

Advertisement NovaTech
Advertisement SkyTale Software GmbH
Advertisement Northrop Grumman
Advertisement
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
0