Both times I have done Celebrity cruises, once onboard they have said there is a disembarkation option that if you are prepared to carry all your own luggage off the ship, you are allowed off first as soon as the gangways are in place. I think you have to be waiting at the gangway door with your bags at whatever time docking is. They haven't advertised this option beforehand as they obviously want to persuade people into buying transfers or post cruise tours instead.
Anyway, as both Celebrity disembarkations I have done have been absolute zoos, coupled with a complete lack of interest - nay, almost contempt - from crew towards pax who are disembarking thus paying no more tips and submitting no more feedback forms, I think if I cruise with Celebrity again I will go with the self-disembark option.