Appointment time will not come back

Hello I am a new user to Appointments +. I have noticed that if I cancel an appoint on the admin side the time slot that was reserved will not become available. Example if someone makes an appointment for the 24 of January for 12:30, they call me and tell me that they will not be able to make it, I cancel the appointment on the admin side but the 12:30 time slot will not become available. Now all these additions of appointments are done at 6am so it is not like I cancel the appointment at 12:30 and expect to see it. Thank you