Michelle, I'm afraid I'm not much help. Most cruises we have opted to stay over one day so we didn't have to rush. I think the only time we didn't was on our first cruise. We took the 1st
DCL bus and we were on the early embarkation (early dinner) so we were out of there by 8:30 AM. We made it in plenty of time for the plane, but then the plane was delayed for over 6 hours!!! However, that was back in 2000 prior to all the changes after 9/11.
We were concerned about the Labor Day exodus as well. That's why were spending one extra day. DH wanted to go to Aquatica since the kids and I had such a great time in May . .. we wanted to do it again (and it's free with our BG passes .. . Yeah)
I'm sure it will work out for you. Most security is understanding about which flights have to leave soonest