We did GMFB in August when the park officially opens at 9am. We waited by the security bag check gate until 8am, when they started to let us in. We walked to the restaurant and were there by about 8.15am. Had breakfast (quickly) and were generally waiting for Dumbo to start by 8.30 or so. It depends if you can get there for the very start or not I suppose!
We did think about doing the rides first and breakfast second, but reasoned that if we are eating breakfast at 9am+, lots of people are entering the park by then and taking up valuable ride times!