The answer is printed on your paper or PDF statement every month. The cancellation period is 45 days from the date of the statement on which the Renewal Notice appears. That's one statement before the one on which the fee is billed. This effectively gives you 15 days from the fee billing statement date.
Thanks and I did see that before for other players. However, I noticed a recent comment on Doc about an online cancellation stating 40 days from billed date.
*Update: Called a phone agent today who also stated 40 days from AF posting date.
AF Posted 3/24. Renewal notice statement posted 2/21. System generated disclosure read by the agent stated as long as AF billed after Feb 25, AF will be refunded.
*Update: AF successfully refunded when closing 21 days after posting date. It appears the 40 day window from AF posting date clause from numerous agents is true.