I'm pretty sure it is 8:00 also, and it being a buffet it is really quick. We actually had 10:10 am reservations in January, and were trying to get there early to do KS before breakfast. I guess we were too excited, and got to the park a few minutes before 8:15. We decided to try to eat earlier, and they actually let us into the park since we had ADR's, with the warning that we had to go straight to the restaurant, no other loitering. Not a problem, we were seated about minutes after checking in, and out by about 9:15 to 9:30. It was nice to just get it our of the way, and not have to rush back.
We also did that at DHS one morning; had 8:45 resevations at H&V, and got there about 8:00, and got in quickly, and were out about 9:15. It really is much less crowded the earlier you go, and much more enjoyable.