Magical Express runs back to the airport as long as anyone needs it. But ME is meant for guests staying exclusively at Disney's resorts.
I would cautiously suggest that you find some flight, any flight, any airline, that leaves that night before and that you reserve your ME trip back so as to make sense with catching that flight. That means you leave your resort 3 hours before then.
I don't think any flights are scheduled to leave after midnight so you can't stay for Extra Magic Hours that late.
Disney hints:
http://members.aol.com/ajaynejr/magicx.htm
Because guests with early morning flights need to get up at some God awful time to catch ME early in the morning, it makes sense for guests to be able to stay the last night at an airport hotel, taking ME the night before. But ME might not be intended to run that late normally. I would not discuss this subject with CM's near the end of my vacation, the CM's could come out and say the trip doesn't qualify for ME, end of conversation. Wait for someone else to raise the issue by mail and for the answer to filter down through the grapevine called The Dis.
