I'm glad the author made this point and backed it up with a reference. It reaffirms something I already believed (whether on the basis of personal experience, something I'd read before, or mere wishful thinking, I couldn't tell you so the reference helps). It is a sensible constraint that came to mind in reading all the tech workplace horror stories that the Times's Amazon piece inspired.
While reading that Times article I checked out the link to their 14 sacred principles. The funny thing was that I agreed with most of them. They were all ideas that occurred to me over the course of my career working independently, with small companies, and especially now in corp.
The one thing that was missing, I felt, was a Rule #15: Never work more than 8 hours a day.
Without it, it's no surprise you end up burnt out or living in the sort of dystopian workplace documented in the Times' Amazon article.
But then I suppose, as has been pointed before, long work hours are more about cultural signaling and penny-wise-pound-foolish accounting than really improving productivity.