Not so. Once the first guest boards a DME bus, the procedure is for the bus to leave no more than 15 minutes later, even if there is only one family on the bus.
Otherwise, the bus dispatching is based on need, and they know the approximate need because they have reservations, so they know about how many people are going to need to go to which resorts at about what times. For example, if there are NO reservations for anyone going to Wilderness Lodge before 3:00 p.m. today, then there won't be any buses scheduled to drop people off there until that time.