Historically, USNA does an accelerated schedule on the Wednesday before Thanksgiving, which means that classes will be done by 1230 (Maybe? Don't remember anymore). If a mid doesn't have afternoon classes though, they can leave after their last military obligation. Usually they have to be back by 1800 that Sunday.
The official policy when I was a plebe at USNA (which is now two Dants ago) was to schedule a return flight that returns at least four hours before the End of Liberty (EOL) formation. Otherwise, like if you schedule a flight returning at, say, 1630, and it got delayed/cancelled, the MIDN could be held responsible.
On the front end, allow at least two hours to get to the airport and check in.
If any of this has changed, the administration will probably put out info fairly soon.