This is true of the UK, and I guess will work in a similar fashion across the globe ....
Most lines have what is called 'self help disembarkation' which allows you off the ship as soon as all the customs formalities have been completed. HOWEVER you MUST be able to carry off ALL your luggage with you in one go, you will not be allowed to return to the ship to collect more, and will not be allowed to put your luggage out the night before to collect in the shed as you pass through it.
The other things to consider are the transfer time to the airport & the check-in time at the airport, with possibly long queues as well.
I would defiinitely contact
(a) the cruise lines to see if they do have self-debark & what you have to do to apply for it. If you can get their authorisation in writing before the cruise, then do so, just in case the front desk aren't aware of the system.
(b) the airline for check-in information
(c) a cab coompany to book the transfer & find out transfer times in what could be the rush-hour.
Last Cruise: Azamara Journey August 2014
Next: Queen Victoria November 2014
Followed by: Queen Elizabeth December 2014 and Minvera April 2015
Golden, Grand(2), Caribbean, Sea(4+1 aborted)
Adonia(4+2), Arcadia, Artemis(2), Aurora(5), Azura(2), Oceana(3), Oriana(11), Ventura(2), Victoria(5)
QM2(2), QE2(9), QV(5), QE, Caronia(2), Minerva II, Fred.Olsen(8), NCL Jade, =X= Eclipse, HAL Ryndam, Aza.Journey