Effects of Scheduled Overtime on Labor Productivity: A Literature Review and Analysis

All sources, except one, report consistent conclusions that efficiency is impaired as the number of hours worked per week increases, such as, scheduled overtime causes a loss of efficiency. (SD-60, p. 48) 

The results from analyzing the length of the workday were mixed. In some cases, the data showed that loss of efficiency was unrelated to the length of the workday. In several other instances, there was a near linear relationship between the loss of efficiency and the length of the workday. (SD-60, p. 6)

The results from analyzing the number of work days per week on efficiency were mixed. In two studies, there were differences of about 7 percent (absolute) in the 6- and 7-day workweeks. In two other studies, there were no differences or they showed the 6- and 7-day schedules to be slightly more efficient than the 5-day schedule. For one study, the results were erratic. (SD-60, p. 34)

Determening the point of no return was simply a mathematical exercise based on efficiency curved. The point of no return is no more accurate than the efficiency curves themselves. Several reports stated that overtime should not be continued beyond two-thirds of the point of no return. The literature suggested that the point of no return for construction was considerably longer than in engineering work by a factor of 3 to 4. (SD-60, p. 43)