Yes, you will be allowed in early for the breakfast. We had a 9:00 reservation last Tuesday and were let in the main gates at about 8:15. We hoofed it over to Norway and were the first to check in. They invited our 8 year old DD to be the Princess of the Day; they decked her out in a princess cape and hat and she got to open the restaurant at 8:30 with a magic wand. It was quite a thrill. They also prepared a beautiful "Magical Moment" certificate for her that all of the princesses signed.
This was our second time doing the breakfast and it is our favorite (better than Cinderella's in the castle, we think). Last Tuesday, the princesses were: Aurora, Belle, Snow White, Mary Poppins, Mulan, and Jasmine. A stellar cast!
We went in the main gate, but I'm sure they have people ready to let you in at the International Gateway as well.
Have fun!