If you have the option, from Nassau I'd want to visit Allen's Cay
which is uninhabited but has an endangered iguana species there.  I
know there are trips from Nassau, but I don't know if it is an option
given the time frame.

For St. Thomas,  it is recommended by most people that you take a cab
from the dock to Red Hook and take a ferry from there to St. John to
enjoy the beaches and snorkeling.  Although diving the Rhone is also
nice.


grandma Rosalie

All hard docks and no tenders, so that's nice.
Try this site for port info:
http://www.cruisecritic.com/ports/area.cfm?area=8

You don't want to dive San Juan, and you can't get to any decent spots,
dive, and back to the ship in that time span.  You can walk around Old
Town (no tax on purchases is nice) and see the Fort easily enough on
your own.  Don't bother with the rum factory tour, no one I know thought
it was worth it.  El Yunque tour is nice if you'd like to see a rain
forest, but is alot of time on a bus with alot of other people, much
better if you can arrange another way of seeing it because you will have
more opportunity to get off on a trail.  Luquillo beach is conveniently
near the entrance to the rain forest (about a 45" drive east from San
Juan) Don't do the snorkel/kayak trip to the Fajardo area, it isn't
worth it.

Nassau, dive for sure.  RCCL hooked us up with Nassau Scuba Centre
http://www.nassau-scuba-centre.com/ last year, the guys that booked it
on their own paid 5 bucks less than we did at the time and we all shared
the same van out to the opposite end of the island for the dives. Might
have to watch your time frame here.  Nice op overall, had fun. First
dive was to Sea Viking at 80fsw for 40 min. and doing a safety stop is
mandatory or else you won't be doing the second dive, as one person on
our boat soon discovered. SI was 40 min.  #2 was to Bahama Mama
wreck/sharks at 53fsw and 50 min. BT. If you have time, which I doubt,
grab a 7 minute cab ride to the huge Atlantis Resort from the ship's
hard dock and take a stroll around the massive resort/casino/aquarium
complex. You have to pay for a real tour, but we saw enough without
doing so.

St. Thomas, 4 years ago, Underwater World. 16 divers in 2 groups and 2
40 minute dives to 74fsw and 60fsw.  #1 Buck Island-Snapper Valley, this
must be where they take you to see if you crash into the reef or
something, didn't see much.  #2 Andre's Reef (they must have decided we
were ok), dive site better all around for soft corals, sea life and viz.
 SI was 35 min.  I could have done better on my own since it was an
early arrival, and the ship may be using someone else now.  I've taken
the ferry to St. Johns where there was a nice secluded beach, but
there's plenty to do on St. Thomas since it's your first visit. Just the
ride around the island can be an adventure, keep appendages you want to
keep in the vehicle ;)

St. Maarten, everyone told me to skip it or go to Saba.  So of course,
last year I dove it anyway since Saba required a short flight over and
there were time constraints.  Dive Safaris was the op and this was the
same trip that we went to Nassau.  #1 Fish Bowl at 59fsw for 47 min. #2
Maze was 52fsw and 52" BT.  It was enjoyable, not as nice as Coz or
Cayman, but I'd dive with the op again.  Unfortunately I still had
enough time to spend $$$ on Dutch side for electronics.  Easy to catch a
cab/van to the French side for the beach on your own.

Have fun planning it, you have alot of time.