My suggestion, in that case, would be:
Hop a yellow cab to the Zona Romantica in the A.M. Explore the shopping areas nearby. Have lunch at one of the beautiful and excellent restaurants on the Cuale, such as Le Bistro or River Cafe.
Then hop a cab back to the Krystal for an afternoon in the sun. You can stay there right up to the last minute prior to sailing, with no worries about getting back through traffic jams and such. Plus P.V. can get kind of warm, so morning touring and shopping would be much more comfortable.