Yes. We had an 11:50am flight after our Fantasy cruise a week ago, and even stayed for late seating breakfast with no problem at all. Were bored spending over an hour hanging out at all of the airport gift shops near our gate before boarding began for our return flight.
If the shuttle you're taking is a
DCL transfer & you're not flying Southwest Airlines, I recommend using Onboard Airline Check-In to speed things up at the airport.
If you're doing a non-DCL shuttle & checking yourself & your bags in at the airport, then I recommend leaving the ship shortly after it opens up, just to give yourself plenty of time.
But either way I wouldn't hesitate to book an 11:55am flight out. That's the ideal time IMO.