My dh and I left WDW on two different dates and neither one of us got that night before envelope...he left from BCV and I left from POR. He had only carry-on luggage and was on a bus at 8:30 for a 11:30 flight.
I checked in with DME about 8:45 on my departure day, checked my luggage and got my boarding passes. I went to Bell Services and they gave me the voucher for the return trip on the bus since I had stupidly left my DME packet in my checked luggage!! DME will usually have you on a bus 3 hrs. before your departure flight time. Be sure to check in with them as early as you can.