11 might a bit close. I would say if you have a car service and do Express Walk Off you should be fine. The only caveat is that, depending on when you are going, Galveston is sometimes besieged by fog. I've cruised out of Galveston three times, and other family has cruised out of Galveston 8 times, and out of those 11 times, only twice has the ship (not all Disney) actually arrived back to Galveston on time. Anecdotally, I think January and February are the worst for fog.