Are you flying into Orlando Airport? Are you staying at a Disney resort (not including Swan, Dolphin, Shades of Green, Bonnet Creek, hotels on Hotel Plaza Blvd)? Is it more than 10 days in advance of your trip?
If so can you get those Mears transfers refunded? You could then get Magical Express which is free.
For Mears' regular service, you or your
travel agent should try to make a reservation at least a few days in advance given your late arrival time. I am not sure of the operating hours but the agent on the phone may say you do not need a reservation. When you get to Orlando Airport, get your baggage and then ask for directions to the Mears desk. There is a Mears desk on the "A" side of the main terminal on the lowest level. You must go to this area if you do use Magical Express. On the "B" side there is at least one Mears desk outside.
You may be put on the same bus as Magical Express guests if you are going to a Disney resort.
For both Magical Express and Mears' regular service, reservations are required going home and at Disney resorts this can be handled by the Magical Express desk. Going home, you may not check bags at the resort airline check in stand since you must have your bags in your hands to go through customs at the airport.
Disney hints:
http://members.aol.com/ajaynejr/disney.htm