" One study, on construction projects, found that “where a work schedule of 60 or more hours per week is continued longer than about two months, the cumulative effect of decreased productivity will cause a delay in the completion date beyond that which could have been realized with the same crew size on a 40-hour week.” In a very different industry, a software developer notes that when his staff began putting in sixty-hour weeks, the first few weeks would see much more work getting done. But by week five, the employees were getting less done than when they had been working forty-hour weeks. "
― Sendhil Mullainathan , Scarcity: Why Having Too Little Means So Much