I am headed to the Grand Floridian for a conference. My DW and DD are coming in the last 2 days and then we are driving down to Ft. Lauderdale for a cruise. I need to rent a car vs. taking the magical express. But my DW and DD will take the magical express to the resort when they arrive. So I would only need a car seat for 1 day of my week long rental. If I go over to the car care center to pick up a car seat does anyone know if they just charge me for the one day or do they back date it to the beginning of the rental period?