For lack of a better thread to post in...
If you are landing evening time about 6pm @ FLL, you can check for the 489 SE 17th St which is the off airport location pricing for sixt - as their pricing is sometimes cheaper than the airport. Make a res there for 6pm on the button (they close @ 6pm so making a later res will be rejected), and their policy is that if you cant make it to pick up the car until after their branch closes(6pm), you can pick up at the airport. Once you pick up at the airport, at least IME, they allow you to return to FLL location as well. The rental rate will remain the rate you originally reserved at.