What happens if I arrive earlier or later than booked?
Don't worry if you're not bang on time, most car parks and hotels expect this and will help you as best they can.
For car parks where someone does your actual parking (e.g. Meet & Greet), it's best to check the contact details on your booking confirmation and call them beforehand, to let them know when to expect you. Otherwise, park as normal.
It's at the car park's discretion if they charge you for any additional time if you do arrive outside of your booked times. They usually charge their standard rate (there's more information on rates on your booking confirmation).