What do I do if my flight is delayed / cancelled?
Don't worry if you arrive back later than you've booked, most car parks and hotels expect that you won't be there bang on time and will help you as best they can. Where you have booked a car park which needs to arrange a driver for you, such as Meet and Greet, just give them a ring so they know when you're expected - their contact details are on your confirmation.
Any extra parking charges can be paid at the time to the car park directly. Unfortunately, it's not possible to extend a booking once it has started.