You can edit the duration to which your online booking cancellation policy applies.
Phorest, by default sets the cancellation period to 24 hours which means that if your client cancels their appointment within 24 hours they can be charged up to 100% the value of the booking.
To edit this change, go to Manager then Settings.
The choose Online Settings and Booking Rules
On the Cancellation Period type in the cancellation period e.g. one Day = 24 hours, 2 days = 48 hours etc.
You have now updated your cancellation period for Online Bookings.