I have made flights as early as 10am out of Ft. Lauderdale, but only when we have disembarked from Port Everglades in Ft. Lauderdale. You do have some things working in your favor. Depending on what airline and cruiseline, there are ways to really speed up your disembarkation and airport check-in. First, most cruiselines have a self-debarkation policy, which allows you to walk off the ship right away with your own baggage when the ship docks. You just need to let the cruiseline know ahead of time you have an early flight and need to disembark early. Of course this is dependant on the number of bags you have and are you able to do this.
Second, most airlines allow you to check-in online up to 24 hours ahead of time. You can use the onboard internet cafe to do this. Third, depending on the airline, most have self-serve kiosks for baggage check-in, so if you check-in for your flight onboard and use the quick self-serve kiosk to check baggage, you can save some real time there, but only if your airline offers those options.
Now a few things working against you. The biggest being getting to the Ft. Lauderdale airport from Miami. If you use a shared shuttle, even if you are able to disembark quickly at 8am, the shuttle might not leave right away until they have more passengers. So you might have to shell out more money for your own dedicated shuttle or a taxi which is going to be very expensive. Second, the traffic is a big variable between Miami and Ft. Lauderdale. One accident or traffic jam, and no way you make it. And now the biggest variable of them all, the security lines at the airport. While they usually move quickly, now with the increased scrutiny following the Christmas day incident in Detroit, it is likely to take much longer now to get through security.
Also, check with your airline and see what flights are available later. If you miss your 11am flight, are there later flights they can get you on? Dpending on who is working the counter for your particular airline, sometimes they can take pity on you and give you seats on a later flight if you miss your 11am with no problem or extra-charge, or maybe they play hardball and charge you 1 arm and 2 legs.
One option for you, depending on flight availability and price, is to book a later flight. Then still try to make the 11am flight. If you get to the airport in time and the lines are not long and there are seats available, the airline can put you on the 11am flight. Airlines allow you to go standby on an earlier flight to the same location if you have seats on a later flight for no extracharge.
So bottom line, I probably wouldn't book an 11am out of Ft. Lauderdale unless my ship was docking in Ft. Lauderdale. But it is up to you to weigh the variable here and decide. Either way, good luck!