Ideally if you can get and accept a retention offer the first year a couple of days or a week or two prior to AF posting that's the best. This way 13 months later you can still try for another retention and close the card if you don't get one for a refund of the AF.

If you accept a retention offer after your AF posts up to 30 days thereafter, you can still close the card 12 months later for an AF refund but will most likely not be eligible for another retention until 13 months have passed at which point you will no longer be eligible for an AF refund as you will be past the 30 day window for that.

In my case, I was outside of that window already when I originally accepted the retention so I plan to downgrade to the green if no additional retention is offered and at least get a pro rated refund. If you're ok with that then you can go that route any time the 13 month wait period exceeds the time eligible for a full AF refund.