Upvote:4
There is no etched in stone schedule. Airlines open up flights for booking 330 days ahead (a few earlier, but 330 is the most common). They tend to not offer a lot of seats in their cheapest fare buckets initially, as they prefer to sell seats at a higher fare.
If seats are selling well on a flight, they might not release any of the cheapest fare bucket. If sales are sluggish, they will open up some seats at the lower cost fares.
Available seats within a fare bucket can be adjusted daily, weekly, monthly, maybe for all flights, maybe for only a couple of dates. It is a complex process that few outside the industry can decipher.
If they had a strict schedule then folks would wait until a certain date to book the cheapest seats. So they deliberately keep you guessing.