EE is officially 1 hour before the park opening time, so in most cases 8:00 a.m. However, during our last trip, Epcot pushed it back to 7:45 a.m. one day and even as early as 7:35 a.m. one time. MGM, AK, and MK seemed to stick pretty close to the 8:00 a.m. time, although they might "fudge" a little and open a few minutes early.