DCL wants everyone off the ship by 9 am. It is about a 45 minute drive to the airport.
Your breakfast time on the last day is determined by your dinner seating. If you have late seating, you will have 8 am breakfast. I really don't remember what time early seating eats, but it is before that. Alternatively, you can eat at Topsiders.
The only kicker is that from the time the ship arrives in port until it is "cleared, it is under the control of US Customs, Not DCL. Until Customs clears the ship, DCL cannot open the big doors. Normally, the doors open about 8:15 ish. However, there is always the possibility of a delayed clearing.
There is virtually no time delay between getting off the ship and getting thru customs, you then proceed directly to your transportation. A private limo should be there waiting for you. If you have DCL transfers, you may wait a few minutes till the bus is full (usually only a few minutes). The whole procedure is that you disembark, go to a luggage holding area where you claim your bags (they are arranged in order by cabin and are easy to find), a porter comes over and loads them on his cart and takes you thru customs (the bags are not unloaded). You and the porter then proceed to your transportation. Total process takes about 10 minutes.
We've sailed on the Magic 12 times. One time, the doors weren't open till well after 9.
So...under normal circumstances, you will have no problem getting to the airport by 9:45 (2 hours before 11:45 flight). I've been at the airport as early as 9 am.