The amount of time it takes to walk off can vary. On two Disney Magic cruises, we had late breakkfast. Each time, we left the dining room before 9 a.m. The first time, we walked right off. The second time, we waited in a long, slow line (30-45 minutes) to get off. Both cruises were post-9/11.
Keep in mind that you are processed by US Immigration officers as you exit into the terminal. There can be a backup.
In any case, there should be no problem catching a 1 p.m. flight out of MCO.
Unless someone is in a huge hurry, there is no reason to skip a real breakfast in the dining room, served by your dinner servers, on debarkation morning. It's the time to say goodbye to the servers who have taken care of you all week. And it's an opportunity to have one last pleasant experience on the ship.