I would think you should have no issues entering early with the confirmation number of your Reservation. Despite the fact that the "Opening Show" may end before the official opening time, the fact is, if your reservation is for 9 AM (The official opening time of the park), I would think you should be AT the restaurant by that time, assuming the park "Officially" doesn't open until 9 AM, I think they would allow you to go in early. If I were you, however, I would plan on being at the gate as early as 8:30 (if not sooner) so that way when you get in you can enjoy Main Street for Excellent Photo ops without a crowd. We did this one year and have our Kids with the Castle in the background and NO ONE else in the picture. It was kind of awesome.