You can cancel at any time and will not be billed any further.
If you subscribe to the yearly or quarterly plan and cancel before your billing date, your refund will be prorated to the monthly rate.
For example, if you subscribe on January 1, 2017, to a yearly QiT at $1344.00. Cancel on May 30, 2017, (5 months access) your refund would be
QiT monthly rate $149.00 * 5 = $745.00
$1344.00 – $745.00 = $599.00