North American airfares are now published four times a day during the week, after the Airline Tariff Publishing Company (ATPCO) added earlier this month a filing feed at 4 p.m. Eastern time to the already-existing feeds at 10 a.m., 1 p.m. and 8 p.m.

This means that, at any of those times, a certain fare can be put on the market, changed or pulled off the market. It also means that a fare’s entire lifespan can be as short as three hours. The 4 p.m. feed had been planned for months, as I wrote in my book “Decoding Air Travel.” Although the airlines update their data 24 hours a day, ATPCO sends that data out to Global Distribution Systems (GDS), which are used by airlines and travel agencies to book flights, four times a day during the week. On weekends, there is only one feed at 5 p.m. ET…