You can cancel a license via your control panel.

If you cancel the license at the same day of the purchase, you will receive the full amount refunded on your account balance.

PLEASE NOTE : 

This is not within 24 or 12 hours, but the same day.
If the license is purchased at 22:00, you can cancel this until 23:59 in order to receive the full amount refunded on your account balance.

This refund is not applicable for renewals.