Return a car and payment

Final settlement occurs on

return of the vehicle.

  This takes time!
Therefore it is not necessary to come to the airport an hour before departure in the hope that you will be free in a few minutes.
The company must inspect the car for damage and sign the appropriate paper and only then you will make the final payment and close the deal.
By the way, most companies require you to return the car with the same amount of fuel, which was taken as well as clean inside and out.  Otherwise, you can deduct from the cost of cleaning and the missing gasoline.