This set of comments by John Carmack on shorter vs. longer work weeks seems sensible (I also wrote something, but shorter, in https://www.patreon.com/posts/61804963, before I saw his comments).
I'm not personally a fan of working long hours, but a lot of the arguments that shorter hours increase output feel like motivated reasoning, where people feel compelled to argue that the thing they want to do is best for productivity (as for me, I'm fine with not maximizing output)
@danluu Exceptions to this are cases where the overhead of having full context and concentration are high, so an intense effort would be a shorter number of hours than regularly paced effort. Robert Louis Stevenson famously wrote "The Strange Case of Dr. Jekyll and Mr. Hyde" in under two weeks.
