I've always rented the car for 8:30. It really didn't matter what time we got at the car rental, there was always plenty of cars waiting. Most of the time, we don't eat breakfast on the ship and leave when they clear the ship and let people off. That way, we don't make it harder on ourselves by wanting to stay on the ship for another cruise. We get the car and usually are in Orlando by 9:30 with the whole day ahead of us. If anyone is renting a car from National Car Rental, be sure to check if they offer a free shuttle to the port. Last time, I booked National because their price was lower than others, but made up for it by having to take a taxi - no free shuttle.
Bev