Your pickup will be something like 12:30. You should be ok with a very early breakfast most anywhere on property BUT you need to realize that if your assigned pickup time is 12:30, you must be at the pickup point with your entire party plus any luggage you are carrying with you no later than 12:20 and I'd suggest 12:15. The ME pickup time is the time the bus will depart your resort, and if you miss that bus, ME might try to get you on a later bus, but if they're full they won't be able to do it. Once you miss your scheduled departure, ME is under no further obligation to get you to the airport in time for your flight.
Depending on how far your breakfast is from your resort, it can take up to an hour to ride Disney transportation back to the resort from wherever it is you are having breakfast. Therefore you need to plan to book a breakfast that will be over by 11 to 11:15.