Approximately 4am if you have a domestic flight or 3am if you have an international flight.
If you call to book Magical Express they can generally tell you what time.
You will also receive a packet hanging on your door the evening before with the paper you need to hand them and it will have your time on it.
If you don't receive that paper you need to go to the desk and have them print it for you since you need to hand it in to the bus driver.