Yes, you can set up multiple reminders for an appointment, at the following intervals prior to an appointment:

7 days
5 days
3 days
2 days
1 day
2 hours
1 hour

For example, you might want to send an email reminder 7 days prior to an appointment and an SMS reminder 1 or 2 days beforehand. To do this, simply create two separate communication triggers for the reminders you'd like to send:

Please note that reminders are saved against the appointment at the time it is booked.  If you set up a new reminder, any appointments already in the diary will not be sent that reminder.  They will only be sent communications that were present at the time of booking.  

Related article:

How do I set up an appointment reminder?
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