If, assuming, your DME pickup time is 8am, I would imagine your flight departure time would be about 11ish. As already noted, you have to be all checked in, bags tagged, boarding passes in hand, and walking away from the RAC counter, no less than three hours before your flight departure.
So..if your pickup time is 8am, I would plan on getting the bags down to the RAC counter by 7, maybe even by 6:30. After about 7:15-7:30, the lines start to get longish...people are dropping their bags off on the way to early breakfasts or before they get the buses to the parks for EMHs. Beat the crowd and get there before 7.
Then...be at the bus stop at least 15 mins before the DME pickup time you are given. That time is the time the bus departs, not the time you should head over there!!! The bus will leave without you!!