It's approximately 3 hours before scheduled departure.
The reason I said "approximately" is that if you have an 8:30 p.m. departure and other guests at your resort have departures at 8:15 p.m. and 8:25 p.m., they aren't going to send three different DME motorcoaches.
You can request an earlier pick-up time, which could be good idea if you want to guarantee enough time for a table service dinner at the airport.