Average Workweek

The BLS publishes data on the length of the average work week. Here it's charted by Visual Capitalist:

 

There isn't much theory about how this does or should behave. There's two things interacting here: how good is business, and how timely is hiring. 

If business is improving faster than hiring, it goes up. If business is not as good as hiring, it goes down. 

Recessions show as deep valleys because, believe it or not, firms actually try to hold on to employees (because they have a lot invested in many of them).