Take the bridge on Key West towards the shrimp boat docks. Eat shrimp steamed in Heineken and conch chowder at the Half-shell Raw Bar. Say hello to my brother and sister Coast Guardsmen right next door. Head towards Mallory Square and visit Fat Tuesday's for whatever frozen drink you can imagine, then rent a jet boat (NOT a jet ski) at one of the resorts (I can't remember the name) next to the Square. 2 hours is plenty. Make it back to watch the real show that is sunset at Mallory Square. After that, visit Sloppy Joe's if you love crowds ( I prefer Fat Tuesdays so I can walk around) or another bar if you want to sit. Everyone is easy to talk to; just ask a question and enjoy!
Like to fish? Stop in Islamorada and do a charter, inshore of offshore. Shark fishing is great, best place for hammerheads I ever saw.