That sounds different from the cruise we took. Seems like we had different arrival and departure times for each island. Mine was not really a kite trip though, just brought gear along in hopes to get out.
The biggest thing is getting to a decent spot to kite from the ships port, which is nice to have a game plan ahead of time if you can. How far from port is there a kite-able spot? Is there a good way to get there? Can you get back easily?
Antigua was nice because Jaberwock beach was a 15 min cab ride from where we ported. The driver agreed to come pick me up at a certain time. Tried to get out in Nassau, but when I got to the beach that I had researched out online (forgot the name of the beach), the tide was out about a mile.
I told myself that when I ever go down that way again that I would pick a good spot and just stay there.
Like you said the ship departs around 5 or 6, I think they want you on board 1 hr prior to departure.
What if the wind picks up around 3?