When the timer expires, or when you (the member) sign off. If more time is needed, the provider will ask if you would like to extend the appointment, which will deduct the appropriate amount of tokens from your account.
You will be reminded as your appointment time is drawing to a close. You are expected to understand that the allotted time is all you have with the provider unless you submit tokens for another time slot, based on provider availability. If you want more time with your provider, it may or may not be consecutive to the appointment in progress depending on availability.