They should begin serving breakfast at 8AM. As with all theme parks, restaurants do not open earlier than their normal scheduled time on EMH mornings so it should still be 8AM.
I personally would not spend an EMH morning in a restaurant. Those parks get crowded quickly especially on EMH mornings. The one morning we did a theme park character breakfast was at DHS, before rope drop (non-EMH morning), and we got out in time for rope drop, got FPs for Toy Story Mania and everything worked out as planned. Just a suggestion!