Our experience with this was:
We made the earliest seating, which was 8:10, and AK was opening at 8:00. It was not EMH, but extended hours for spring break (8-7). They had everyone line up with the mobs of people at the far left line that had PS's, and then opened all the gates all at once. This made no sense whatsoever because we were in the far left and had to go all the way to the right and cross all the people that were headed straight for the safari. Then, when you managed to fight through the crowds and get through the mobs of people, your seating was based on when you checked in. Dh and I, pushing 2 strollers, didn't get there as fast as others and had to wait about 20 minutes, when people with 8:20 and 8:30 PS's had already been seated. They weren't letting 9:00 PS's check in yet. I wouldn't even bother doing this early unless you can get in before the park opens.