I agree that the center should not spring new rules on you like that, but should try to give some advance warning (at least a day) if it is a schedule change. (Not sure if I understand that this was a new rule, not something you might have been misinterpreting...)
If a child arrives here after 7:40 I don't serve breakfast.
I would clarify the expectations with the center, and feed your son at home if they do not offer breakfast as late as you would like. I like doing an early breakfast because it starts my kids with the habit, as when they start actual school it will need to be early. Good luck!