Is this activity based on an assumption that the mission flies as scheduled, or has the decision already been made and NASA are simply waiting for the appropriate committees to rubber-stamp it?
I would assume it moving the SSRMS into position, since it is something that needs to be done, was simply convenient to do now, and that they don't have any other high priority robotic ops planned that would require it to position elsewhere. There's little reason not get simple tasks like this out of the way early
The final launch decision is, as always, dependent on the reviews, both at NASA and less formally at SpaceX. It's not a rubber-stamping formality, but part of everyone involved making sure everything is really ready.