Usually, the wind doesn't come up until later in the morning, so I'd vote for the 11:30 slot if you can talk your wife into it. I think she'd have a great time, she can be a cheerleader like I was if she doesn't want to sail the ship. I was too afraid I'd mess something up, but they have a very well-trained crew on board with you. Marigot is a nice area and since you're on the island, might as well visit it. I haven't done the Art tour, but there are some very talented locals. My favorite is batik, but not sure if they do it on St. Maarten.
Buck Island snorkel is a very good snorkel, we saw turtles, plenty of fish, nice coral, clear water. We went on a catamaran once and a sailboat once, the trip over and back was as good as the snorkel. Both my hubby and I love sailing. Christainsted is about the only thing on the island of any size. The walking tour shouldn't be too long, but should give a good over view of the island's history. You should be able to get in both excursions without any problem.
Hope this helps a little.