We did the morning one; we gathered on the ship at 7:45 and I'd say we were back around noon, so that would be 4.25 hours. Keep in mind that Tuesday/St. Maarten is tropical night, so it's not like you have quite the level of dressing as on formal or semi-formal night; also, if you know you will be rushing a bit when you return, you could have things ready in your room for a quick shower and change. That assumes you have early seating; if you have late, it's not even an issue. We thought the morning sail was perfect, as it gave us time to play in the afternoon; you might consider simply doing the morning one.