We did several pre park opening ADR's (anywhere from 8am - 815am). At every park, there is a character breakfast line. Some places check you name/reservation, others don't. We were let through the gates around 7:50am.
Get there early enough to go through bag check (if necessary) and then head to the character breakfast line.
No matter what time your reservation - get there so you can get into the park when they let you through the gates - get to your restaurant - check in immediately. Those with latter ressies don't generally try to check in right away - quite often you will be seated earlier. It seemed the earlier you are seated, the better table you get as far as getting through the characters quicker - this is especially important if you have plans to make rope drop.