Given that the wheels up time almost seems to constantly change, it is perhaps not the best estimation of when the flight is actually going to go.
Ive never seen the wheels up estimate in RES, is it in DECS ? In which case not all agents have DECS access.
I know the first I usually hear of a change is from the ops guy saying "they just changed your wheels up time to about 30 minutes from now instead of 1hr and 20 mins. I know when I work our Eagle flights going in to ORD this seems a very common occurence.