Example of RAAN steering (coincidentally with a yaw maneuver that has nothing to do with RAAN target):
No RAAN steering case:
Just look at the red ground track only. Because of a flight azimuth constraint, and a lower target inclination than the azimuth allows, the vehicle yaws left (when allowed) to get to the inclination. The ground track will look identical for launch any time of day. You just wait for the correct time of day to get the desired RAAN of your orbit. Orbit will always be 200 km circ at 65 deg for example. If customer has a tolerance requirement of 0.1 deg, the launch window will be essentially instantaneous. If the requirement was +/- 7.5 deg, then you have about an hour window. No RAAN steering needed.
With RAAN steering:
If a customer still has the 0.1 accuracy requirement, the launch vehicle (LV) can utilize RAAN steering to increase the window (to get more launch opportunities that day, due to weather, anomaly resolution, etc), or sometimes a customer might have the longer window requirement (for the same reasons), and still want/require the 0.1 deg tolerance. In this case, you still determine the window optimal launch time that gets the RAAN you want (the red track), but now the vehicle is targeting this inertial plane. If you launch earlier (Earth hasn’t quite rotated around enough), the ground track will look like the purple plot. If you launch later, the olive track. The vehicle still goes to the same 200 km @ 65 deg orbit, the difference being WHERE you inject in the orbit (lat, long, time from liftoff, etc). The flight software only works for this period of validity that the flight software parameters were designed to. You can launch any time from window open to close. Any second, fraction of a second. Whatever. When you see launches only every minute, or 5 minutes, those are operational decisions, and have nothing to do with the LV capabilities. It just makes life easier for the customer and their ops for post-SV separation.
Atlas has had this capability going back to the Atlas II days. Titan IV had it as well. Delta IV did when common avionics came along.
One other note: You can do “psedo” RAAN steering, by just having discrete, optimized cases, at specific intervals, every 5, 10, or 30 minutes, etc, but then this requires uploading at new flight software parameter set throughout the launch window. Delta has done this. I believe Falcon might or might not have.