Keep in mind that Disney sometimes changes their times. For example, we are going over Spring Break. We currently have a pre-park opening breakfast in MK at 8:15am. Right now it states that the park opens at 9am. BUT history shows that they change the park opening to 7am during Spring Break times to accommodate for the crowds.
So....9 times out of 10, you will be fine, but Disney can change things at the last minute.