Availability can really open up at any time between T-355 and T-1. There is no reliable pattern other than a certain number of seats being available at 9 am right on T-355 (or, in the case of new flights, when they are added to the schedule). My hypothesis is that most if not all availability after T-355 is due to cancellations, which result in the award seat being released back to inventory, and not due to ANA proactively making more seats available. My advice is to keep checking, not just at T-21 or T-14, but every day. I have booked F awards anywhere from 6 to 2 months out just by checking every day.