You should be fine, provided you don't encounter any major delays. The Ft. Lauderdale airport is right next to the cruise port, so its only a 10 minute cab ride once you have collected all your luggage. If at all possible, when I can, I'd go in the day before, just in case..
Anne, you should be fine as long as you experience no major delays. We flew in the day of our cruise for our first 3 cruises. We have found it to be worth the extra money to fly in the day before for various reasons: 1. We are less likely to miss the ship due to flight delays. 2. We are more relaxed since we got a good nights sleep and didn't spend 1/2 the day flying. 3. We get to get on the ship early and RELAX!!!!!!