Some airlines make awards available when they load their schedules, which varies between roughly ten to twelve months prior to flight. They might add seats right when schedules load, or they might wait a few days or weeks.
Other airlines will wait until travel approaches. Although in general I find the best time to be searching for award space is about 6 months to departure. And one of the toughest times is two months out — seats made available in advance may be gone, and last minute award space hasn’t opened up yet.