The service duration field should be visible (without requiring editing).
When the Allow Custom Duration option is enabled and a start time is set, the end time should be automatically calculated based on the service’s predefined duration.
When the Allow Custom Duration option is enabled, time slots where the staff member already has a booking should not appear as available. For instance, if staff member Maria has a booking on January 23rd from 15:00 to 16:00, this time slot should not appear as an available option.
When creating a new appointment, the default payment method should be set to “Mark as Pending.”