We have implemented some authentication steps to the process which will allow us to monitor this issue and respond to any frequent offences.
If you haven't arrived within 15 minutes of your specified arrival time, you will receive a reminder notification with a link to edit your arrival time. If your arrival time has not been updated and you have still not arrived within 30 minutes of receiving this notification, your booking will be cancelled and parking space released back in to the system for someone else to book. This happens automatically.