Having just done this on Sunday, I would say be cautious. We queued at 6:30 but they didn't start letting people off until 6:45 am. Our flight was at 9:05 so we got nervous when we saw that the line went from the Royal Promenade, through the MDR, out the side of the ship and around the back. Around 6:50 we started moving and were eventually through customs by 7:20. We made it to the airport by 7:30 and through security by 7:50. Our plane started boarding at 8:35 so we had enough time for breakfast.
We got lucky though. Allure/the terminal has been having issues with one of the ramps exiting the ship and some of our fellow cruisers reported that the closed a ramp around 7:30 due to it being unsafe for guests to stand on (a little worrisome) which would add a lot of time to the disembarkation process. Customs was fast for us be we had friends on the same sailing waiting in line for 2 hours. Actually, by the time our flight landed in NJ at noon, we still had friends waiting in customs at the port. Crazy!!
You can do it if you have a perfect disembarkation but I wouldn't do it again. To me, it was almost the same amount of stress as flying in the same day. This time we got lucky (and probably avoided weather delays at the airport due to Alberto) but I don't want to end vacation on a stressful note haha.
Good luck! Enjoy your cruise!!!