The <= 40 thing wasn't some random feel-good. Time and Motion and Operations Research people looked at what happened in wartime rush-rush production, and the evidence they collected was (from what i read) pretty good that its a law of diminishing returns followed by a downturn in safety and quality.

My only cite is indirect: Angus Calder "the people's war" but I would be surprised if this isn't well documented in the real literature.

Also, some of the outcomes very quickly become externalities: nobody notices the bodge job until 5+ years later, and people die young of non-specific stress related diseases which don't get attributed to work.