The timing of receiving your refund is affected by if you cancelled within or later than 6 days after you made your initial purchase:
If you cancelled a session within 6 days from initiating the purchase, you are still in a "reserved state", and your refund is processed within one day.
If you cancelled a session more than 6 days away from initiating the purchase, you are in a "charged state", and the refund could take 2-3 days (depends on card and bank),