Earlier quoted context omitted.
I'm curious if the 40-45 hour work week is cultural. Maybe if society was set up for a 20 or 60 hour work week, we'd see the same type of productivity cliff.
Before the 40-hour work week society was indeed set up for longer work weeks, and workers organized to reduce it. There's historical context for many countries given here: https://en.wikipedia.org/wiki/Eight-hour_day
Employment is much more constant in some trades than in others. In the greater part of manufacturers, a journeyman may be pretty sure of employment almost every day in the year that he is able to work. A mason or bricklayer, on the contrary, can work neither in hard frost nor in foul weather, and his employment at all other times depends upon the occasional calls of his customers. He is liable, in consequence, to be frequently without any....
Some workmen, indeed, when they can earn in four days what will maintain them through the week, will be idle the other three. This, however, is by no means the case with the greater part. Workmen, on the contrary, when they are liberally paid by the piece, are very apt to overwork themselves, and to ruin their health and constitution in a few years. A carpenter in London, and in some other places, is not supposed to last in his utmost vigour above eight years. Something of the same kind happens in many other trades, in which the workmen are paid by the piece, as they generally are in manufactures, and even in country labour, wherever wages are higher than ordinary. Almost every class of artificers is subject to some peculiar infirmity occasioned by excessive application to their peculiar species of work.
Adam Smith, Wealth of Nations
https://en.m.wikisource.org/wiki/The_Wealth_of_Nations/Book_...
https://en.m.wikisource.org/wiki/The_Wealth_of_Nations/Book_...