Hi -
I had the same question - here's where I found the answer:
Walt Disney World Resort - Detecting Browser Properties . . .
Specific question:
What are the hours of operation and location of the Disney Welcome Center?
A. The Disney Welcome Center is in the Main Terminal Building of Orlando International Airport on the B side on Level 1. The hours are 6:00 a.m. to 11:00 p.m., but we will be happy to extend those hours if you have booked Disney's Magical Express Service and your flight is scheduled to arrive after 11:00 p.m.
Hope this helps!