There’s a piece in Forbes called Why A Four-Day Work Week Doesn’t Work that suggests:

But there are serious drawbacks. Packing 40 hours into four days isn’t necessarily an efficient way to work. Many people find that eight hours are tough enough; requiring them to stay for an extra two could cause morale and productivity to decrease. As for saving on the cost of commuting, it likely isn’t true.

The article is right: More hours in fewer days is not an efficient way to work. That’s why this article misses the point.

The point of the 4-day work week is about doing less work. It’s not about 4 10-hour days for the magical 40-hour work week. It’s about 4 normalish 8-hour days for the new and improved 32-hour work week. The numbers are just used to illustrate a point. Results, not hours, are what matter, but working longer hours doesn’t translate to better results. The law of diminishing returns kicks in quick when you’re overworked.

Besides, very few people work even 8 hours a day. You’re lucky if you get a few good hours in between all the meetings, interruptions, web surfing, office politics, and personal business that permeates typical work day.

Fewer official working hours help squeeze the fat out of the typical work week. Once everyone has less time to get their stuff done, they respect that time even more. People become stingy with their time and that’s a good thing. They don’t waste it on things that just don’t matter. When you have fewer hours you usually spend them more wisely.

So don’t think 4 days means cramming the same amount of time a shorter week. Longer days isn’t the goal. Think 4 days means a shorter week with less time to get things done. And that’s actually what you want.