You'll need to be very conservative as you won't know your last class time.
Your first Labor day is always harder to predict and the schedules are not posted yet. Always check the USMA parents page for the schedules.
But there is a pattern and you can usually predict enough to book at least the return, and sometimes the outbound early.
Here's the typical 3 day weekend+Monday pattern:
There will be 2-3 buses between 1PM and 4 or 4:30 on the Friday before a 3 day weekend. And 2-3 between 10'ish and 4'ish on the Monday you are due back.
Since you don't know your class schedule, you pretty much have to assume the last bus outbound as a plebe, then 4 hours for transit & airport checkin/security. Some go with less, but we allow for 4 and then go standby for earlier.
On the return we shoot to land noon or 1 to make the 2nd bus easily. Not recommended to count on the 4'ish bus, if you have a flight delay you won't have a backup. Not worth risking, especially as a plebe on your first leave.
It gets easier, and you'll see the patterns. Thanksgiving and spring break are easy, they will be based on the AY calendar. Winter leave outbound is always hard because you won't know your TEE schedule, and it's more than just time, the day can change.
There are exceptions, with last year's Labor day being one due to a Friday football game. No one knew the outbound bus schedules till very late.
In these cases you can go ahead and book the return early, but may have to wait on the outbound until you know more. I'd recommend doing this for Winter leave as well.
It's also worth snagging the previous year's bus schedules from the parent page to keep on hand. They get deleted when the year starts, and they are handy to see typical schedules.
I will say it's a balance, if you try to book too early you can get stuck with a change. Or worse, no leave due to several potential factors. We would book early (2-3 mths) for Thanksgiving as it's a peak travel period and easy to predict. Same for return on winter leave.
For the others, we wait till we know the schedule from the bus schedule and the cadet's plans.