We really hesitate to let the new online booking be activated because email reminders can only be sent 72 hours in advance at the earliest.

In theory, 72 hours in advance seems more than enough. In practice, we do know that not everyone sees and reads their emails immediately, and often only reads them 24 to 48 hours after receipt. In those cases, there is still a good 24 hours (or a little more) left for the hairdresser to fill in a vacant slot after cancellation. That's tight.

In those cases, you could lay responsibility with the customer and charge a penalty or cancellation fee for cancelling too late. Most hairdressers with a thriving business get up to 75% or more of their turnover from a regular customer base. It is up to those hairdressers to charge their regular and loyal clients compensation for late cancellation or rescheduling.

However, if their customers were reminded 5 days in advance, and then only reschedule or cancel 24 hours before the appointment, that would be a little easier.

All understanding that for system reasons, you limit the memories to a maximum of 72 hours in advance, but that is not a little too tight in practice.