I'm 1/2 guessing here, but I think the buses start at 6:00 a.m., I do seem to recall they start with plenty of time to make early breakfast ADRs, but you should confirm that, just in case.
For the ME, when we arrived, we were 3rd of 4 stops (Grand Floridian 1st, Polynesian 2nd, WL 3rd, and...