Of course since weather and traffic conditions cannot be accurately predicted, the times you give at booking can only ever be approximate. The amount of time you need for dropping off your car and getting to the airport will vary according to transfer time. You may find after choosing your car park that before going ahead with the booking you need to modify the drop off and pick up times you originally entered. You can do this simply by going back or clicking 'Change dates'. If you want to change the times once you have already completed the booking, you can do so through your online account (see our FAQs).
You should check the car park operator's information page for any additional advice about arrival/transfer times.
Some shuttle bus services operate to a timetable and others operate on demand: you will need to time your arrival at the car park accordingly allowing enough time to park your car (usually at least 10 minutes).