Where do I setup the time interval for the reminder that sent to the clients in advance of an appointment?

This is done for each specific appointment type in CALENDAR > Appointment Types > click to edit the appointment type > “Reminders” Tab, where you can specify the interval of time the reminder is sent in advance.

This can be set for any/all reminders set for an appointment type, so if you have multiple reminders for an appointment type, then you can set them to go at different intervals before the appointment (e.g., : one reminder with 24 hours and another reminder with 1 hour in advance).

You can also specify the time interval for the reminder(s) in the scheduling pop-up window, for example when – for some particular client appointment – you want to schedule an appointment on your coach end in the calendar.