End of cruise excursions

Any ideas of what to do after docking in Miami, flight out isn't until 7 that evening?

Most ships have tours after getting to the home port. Usually there are 3, maybe 4, tours listed at the back of ALL the tours 'booklet'. Friends took a tour of Southbeach once, maybe a tour of Everglades, etc., and tours usually end at the airport.

Don't pay attention to these tours because we drive to ports.

With that length of time, I'd be tempted to rent a car and drive somewhere. It would be less expensive than taking the ship's excursion. Plus most excursions don't last but a few hours and would still leave you waiting at the airport for five or six hours.