Reviving this thread to update it with what happened in the end, since I always found that helpful when searching this forum for answers

. Kept the 11:45 flight and decided not to plan for the exception. It’s not like we wouldn’t make it home eventually, and I knew I’d be so mad to see that 11:45 flight take off without me if everything went as expected. And it did. On board, our servers recommended the express walk off, and the instructions on the Disney app also recommended it for flights before 1pm. So we had breakfast in marceline market at like 6:30 and got in line to debark. The app did not list marceline as open but our servers told us it would be open at 6:30.
They were ahead of schedule in getting cleared by customs, and we were off the ship by 7:15 (and we were not close to the front of the line). Getting ourselves through customs was a breeze. Boarded a
DCL bus and we were pulling into MCO by 8:20.
Other members of our party with later flights stayed for the first breakfast, and they texted us from their terminal at 9:50, so they had not only arrived but cleared TSA by then. When we boarded our flight, I saw people with the same character luggage tag as us, so we definitely could have stayed for the MDR breakfast and made it. Didn’t want to take the chances with TSA on a holiday though!
Thanks everyone for your earlier advice! Fortunately or unfortunately, since everything went so smoothly for me I guess I’m now hooked on Disney cruises