You can read some VERY funny stories about missing a boat, and you can read some NOT so funny stories about missing a boat...... in a post titled, "Has anyone ever missed the boat in a Caribbean port? What do you do?".... by authors E&M (dated 8/25) on this site.
Rearrange the tight schedule, of course. Don't miss the boat. Miss something else...a few hours of sleep, take off earlier than expected from work or cancel something instead of missing your wonderful cruise ship. Happy cruising.