You can certainly get in earlier than that time frame, however, I'm not sure how much earlier... I know last time I used it, we were there at least 10-15 minutes before Celebrate started and there were already a fair number of people in ahead of us. The FP area for Wishes is typically open for anyone to sit in during the day. I think it closes at 8 pm and I'd guess you can probably go into that area for your FP reservation either at that time or shortly after. However, it's really not necessary. In my experience (unless they've bumped up the amount of people in the FP area) there was PLENTY of room right up to and during the showtime (like enough room that if everyone stood with their arms out, they could spin around and not hit anyone else), so no need to get there super early...