I'd like to see these numbers myself, cause I'm not buying it. The 8 hour workday and 5 day work week has way more to do with labor activists fighting for it than anything else. If 8/5 was truly ideal, and you couldn't argue the numbers, why are Chinese factories pushing 996 (9am to 9pm six days a week). Surely they would have noticed by now all the human errors and fatigue make it not worth it, right?
Even here in the U.S. employers in just about every industry will pay you overtime to work beyond 40 hours per week if it's needed. I've never heard of a manager saying "well, we'd love to have you stick around and help make more widgets, but your past your 40 hours and at this point you'll make too many errors."
Just to be clear, I do think we should go to a four day work week, but I'm not convinced it necessarily is more efficient for any given industry. I just think we should all enjoy more time off with our families.