You can return the vehicle whenever you wish during the booking period, but you will still be charged for the full period. You can also change or cancel your reservation before you take your vehicle, but penalties may apply in the event of late cancellation.
Indeed, you can cancel for free up to 12 hours in advance. Beyond this time, there will be a penalty of 50% of your booking, until the time of booking. If you cancel at the time of booking, you will pay the full amount of the booking.