To build on top of that, I'd want to see how much of that truly free time is in a "high energy state". What I mean by that is a free time where you're awake/energetic enough to do something meaningful – read a challenging book and take notes, write a thoughtful email to a friend, host a party, try to build a new friendship, etc.

On most workdays I find myself so spent that a) I don't want to see people, b) I don't have any mental energy left. I can only do such things on the weekends, but then I'm also fighting with all the chores that have accumulated over the week.

A 4-day work week sounds very appealing because of the challenges mentioned above. An extra day with free and high-energy time would be amazing.