It is generally about 3 hours before your flight. I have used Magical Express 3 times. Here's when I got picked up:
1.) Flight at 8:15pm, picked up at 5
2.) Flight at 2pm, picked up at 11
3.) Flight at 7:40pm, picked up at 4
So, as you can see it's somewhere around 3-3 1/2 hours. The night before you are checking out they come around and put a little paper on your door. This has all the info. about checking out and when to be at the bus. I am not sure if you can get the time ahead of time. Hope that helped...