I also want to know if it's possible to pick up the car later, not earlier ?

When do you want to pick up the car? Just return it at the corresponding time. Don't return it too late.

Sure, we reserved the car for pickup at 10 o'clock. There were a lot of people, so we had to queue up. It wasn't until 11 o'clock that we were able to go through the procedures.

The car has problems when picked up early, but not when picked up late, anyway it won't cost less.