OK, here's his thinking on that one:

He says airlines tend to start fare wars late on Fridays, by Saturday some competitors match. By late Monday - depending on how the new fare is doing - another competitor will likely offer an even lower fare. Matching usually takes place Tuesday, with possibility of lower fares on Wednesday. It's all usually over with by Thursday morning, he writes in his book.

Likewise, he says, fare increases usually happen late Fridays and, if no one matches, come down again early the following week.