I don't ever factor in possibilities of the ship being late. It is such a rare occurrence that to plan for it would be difficult. Where do you draw the line, do you plan on it being 2 hours late, 4 hours or even more. All are possibilities as are weather, plane breakdowns or any other reason for a flight getting cancelled. Too often it's an early flight or much more expensive one mid day or a late night flight that means finding something to do for 8 or more hours so there really aren't a lot of viable options.