We had a similar situation just a few months ago in Miami. We took the bus to the Miami Airport with almost 9 hours to kill before our flight. American let us check our bags 9 hours before our flight. Without bags we took off to run our own excursion on the light rail system. Go upstairs to the free People Mover, which will take you to the Metro Rail station. An all day pass is $5 so you can get on and off as much as you want. We headed south - getting off in the downtown area, at Coconut Grove and a couple other stops. We spent enough time to kill 6 hours before heading back to the Miami airport for our flight and had a great time doing it. Just a suggestion ….