Keep in mind you aren't allowed to linger on the ship on debarkation day, they are literally vaccuming you out. You have to be out of your stateroom by 8am because they do a deep clean of the rooms, change the linens, clean the carpets, etc. so no one can be in those hallways. They have to get everyone on the ship, reset everything and get ready for 4,000 more people checking in within 3-4 hours.
DCL says not before 1 but we've taken an 11am ish flight before, only if we're using private transportation. We almost missed a flight waiting for DCL transfers one time because a family decided to have an argument that held up the entire bus.
You can walk off with your own luggage, which is what we do when we have an early flight and want to get moving, it leaves less chance for delay. You don't have to stop for breakfast but if you want to eat you can always go to Cabanas and grab something from the buffet, you don't have to do the sit down breakfast (which isn't that good in my opinion). It gives you more flexibility in food choice and also with time because it's buffet so you aren't waiting on anyone.