I agree, get to the restaurant as close to 8:00 as you can. I did an 8:15 ADR last time I was there and checked in at 8:00 and was seated almost immediately and we were done and out by 8:40. I'm not sure if they will let you check in 25 minutes early, but you should have no problem with 15 minutes early so even if you have to wait a few minutes when you first arrive to check in closer to 8:10, you should be done before 9:00. The characters at GG come to you pretty quickly because it's not a very big restaurant. We have never gone past about 30 minutes to see them all and when we spend an hour there, we often see them 2 - 3 times each, so that part of the experience shouldn't be an issue.