Maureen,
I believe that the times listed on the itinerary (St. Maarteen 7 AM to 7 PM) are all local time to the island visited. So you should be safe telling them those times. At least that's how it was last year with Carnival.
As far as the suit being too big, it's not that big a deal. It was actually a little large when I purchased it, but I didn't want to have it taken in because of my penchant for gaining weight. But I probably have taken off 8 - 10 pounds since then. Doesn't make a big difference in my appearance since I'm tall, but since the suit was already loose it means the difference between looking decent and being too loose. Aside from which, it's a light colored suit and I'm sure would be just fine, but it seems to me that a dark suit or tux is more appropriate.
MAW - It's a two edged sword. For men the dress code is much more specific than it is for women for all nights. Informal specifies coat suggested, tie optional. Not much ambiguity there. For you ladies you have more of a selection to choose from, but that means more decisions to make. I guess the lack of interpretation of the dress code for us dumb guys helps us out. Hate making those decisions.