Technically, you are supposed to be at MCO 2 hours before your flight. As above,
DCL recommends not scheduling a flight before 12:30.
That said, we had a 12:30 flight, and arrived at MCO a few minutes after 9 am. The airline moved us to a 9:30 flight! We and our luggage were delighted.
If you are not on an airline where you can check in at the port, you can expect a long line for luggage check in at MCO sometimes--we have waited in the line for an hour, but on other occasions it has been more like 10 minutes. If your airline participates in the check in at the port deal, you will get thru the airport security check fairly quickly (10-30 minutes).
Can you make a 12:00 flight? Probably. Can you make an 11 am flight--maybe, especially if you eat at the buffet breakfast. However, when the ship docks, US Customs takes control of it and no one gets off till they say so. While DCL would love to have to big doors open by 8 (and usually does), we were on one cruise where the doors didn't open till well after 9 (and you should have seen the line!) You are safest following the DCL recommendation of 12:30 or later.