We just had that exact scenario last Sunday. We decided to do the hop on hop off tour of Miami. Although it was well done and transportation and luggage issues went off without a hitch, I would not recommend it. We were exhausted by 5:00. You really need to be on the top level of the bus for a good view, but it requires being in the sun and wind all day. There was one place we found on a website called resort for a day or something similar. In retrospect I wish we had done that. There were also some hotels in the area that offered rooms that you could rent for daytime hours, but the hours were still limited for our 9:00 flight.