If you were within 60 minutes of scheduled departure, then this is within the GAs (significant) powers to dispatch a flight. Before that time, however, a domestic flight should not be under gate control. People might still buy that seat, or a pax might switch to that flight with higher upgrade status.

The GAs that wait until T-30 for upgrade clearance sometimes create unexpected opportunities for peeps who know how to game the system. There are methods to "snipe" an upgrade using an alternate instrument in that 30 minute timeframe. To jump the queue so to speak. None of this is against the rules, but it's always interesting to see the last few seats disappear and not go to the top people on the list. For those looking to prevent getting sniped: It's often worthwhile to go to the gate at T-60 and inquire with the GA as AANYC1981 did so above.