Gearshift in Drive and car moving by 4:15 AM for the 7:00 AM flight.
This allows time to refill the gas tank.
Rental companies reserve the right to demand that you show a receipt for refilling within 2 or 3 miles of the airport, otherwise they reserve the right to use formulas of their own choosing to say you owe more for gas. Check the fine print in your rental contract.
We suggest that your refill the tank the night before so, if you are running late, you can skip topping off and only have to pay for a small amount of gas at their exorbitant rates, or maybe pay nothing if you are lucky and the rental agent is not fussy.