I know Cosmic Rays was open earlier than that over Spring Break with Breakfast food. I believe they start serving burgers and such about 10:30, my daughter had one for breakfast one day

it's a vacation

. I also remember some snack stands were open selling breakfast stuff during early EMH. That was in Fantasyland near Ariels Grotto while we waited for Dumbo. I don't know about the other parks because we didn't eat counter service for breakfast.