Hello Mike,
We have the ability to send an email when you create the appointment (which is considered an activity in Method). On the new activities screen, you can check Send an Email?. From here you can select a template and send the client a reminder when the appointment is saved. Unfortunately, Method does not have an automatic timer. There has to be a physical action to all actions. Therefore, you can have a button that when clicked, goes through all the activities and looks for ones in the next 24 hours and sends an email to that client. This is possible. Also, the only way for clients to cancel or reschedule would be from a customized portal screen. I talked about this idea recently in another post that you can check out. Basically, you would need grids, buttons and actions to manage the meetings.
I hope this helps,
Greg