I avoid anything under 5 days so you don't get the "but I just unpacked" feeling when the trip is over. I guess if your near a port it would be good weekend thing.
Do any of the major lines do these trips? I'm guessing the biggest issue would be a minor line having less quality, activities, and a smaller ship that you might be used to.
If it's an option I'd suggest making it a long weekend and just go to the bahamas for 3 nights.
11 cruises in 2012, 90 nights at sea visiting 15 countries
8 cruises in 2013, 56 nights at sea visiting 7 countries
Next cruise: None scheduled
PM me if you need a cruisemate for any Europe, transatlantic, or Panama Canal cruises
Date, ship, cost pp