Cruising the same day is no longer possible. HSA now requires cruise lines to provide a list of all passengers 1 day prior to departure. I have seen that notice on the online pre-registration pages of both Carnival and RCCL. I know that bites, but that's the way it is now.
I may dwell on the land, but I live at sea!
Sensation 2/03 I disembarked, but never really left the ship.
Enchantment 9/03 Just had to go back.
Inspiration 3/04 Just have to go back again, and again, and again...
Sensation 04/05 And again!