Earlier quoted context omitted.
I saw a PBS documentary sometime in the early 90's about the Labor Movement in the US. Just after getting the 40 hour work week, they pushed for 32 hours because it was found to be optimal. Industrialists fought harder against that one so Congress felt it was a worthy compromise to leave at 40. I'd love to find the study the Labor Movement based its conclusion on. My own experience is that I'm maximally focused for 6…
I have the same experience as a mathematics grad student. After two or three hours I run out of focus and need to go for a walk + food.
I noticed the same thing when I was a math undergrad. While working on proofs for Abstract Algebra and Real Analysis, I couldn't go more than a couple of hours.