Give Mike Painting at Lobster Pot a call or email and see what he can set up for you. He runs a great dive op, and works closely with Wall to Wall and Deep Blue as mentioned by
@diversteve. Lobster Pot is my go to dive op in GC, and I usually arrive by cruise ship, and Mike has always set up dives to accommodate my ship's arrival (usually 8AM). Mike does not run cattle boats, and has comfortable dive boats and excellent crews. The last three times I was there, they had a boat go about about 10AM for a two tank dive. I think they also have an afternoon dive, but have never tried that because of the ship departure time. Lobster Pot is a very convenient and easy 8 minute walk to the north from the cruise terminal, and having the three dive ops in the same location makes it easy for Mike to work with the other two ops to set you up if he is full or your arrival time is not compatible. Tell Mike, Guy and several others on SB recommended him. I don't have any vested interest in the company, but I really like them.
GC being a tender port can sometimes be a bit dicey getting off the ship in a timely manner, but you can beat the rush and be near the gangway well before they clear the ship for disembarkation. The ships give tender priority to their excursions, but they can always squeeze in a couple extra people on every tender I have been on.