I agree with this article mostly, although 3 hours a day might be too little to make good progress with work for some people.

This article reminded me of my previous workplace (about 7 years ago) where my manager discouraged engineers from working for more than 6 hours a day. He recommended 4 hours of work per day and requested us not to exceed more than 6 hours of work per day. He believed working for less number of hours a day would lead to higher code quality, less mistakes and more robust software.

Although, he never went around the floor ensuring that engineers do not exceed 6 hours of work a day, and some engineers did exceed 6 hours a day, however, in my opinion, his team was the most motivated team on the floor.