The articles don't seem to give a specific answer (aside from a time and day of the week,) but sounds like the consensus is 3 p.m. EST on Tuesday, your best bet

The articles don't seem to give a specific answer (aside from a time and day of the week,) but sounds like the consensus is 3 p.m. EST on Tuesday, your best bet being 8 weeks before traveling. From personal experience, once you hit the 3 week mark, you're pretty much SOL until the last few days, since most seats have been sold at that point. If there are still plenty of seats (orbitz sometimes shows you the seating chart,) you'll have better results than on fuller flights.