Money buys (productive) time. The manager’s task is to buy productive time as economically as possible.

The most productive time is obviously the day shift, when workers are fully alert and visibility is excellent. The night shift is generally less productive, because the disruption in the worker’s sleep patterns causes them to be less alert and energetic. Also, poor visibility at nighttime slows down the work. So it makes sense to schedule as much of the work during the day shift, and schedule only the most critical and near critical work during the night (so as not to extend the schedule).

Additionally, overtime and premium time costs must be weighed against the effect on productivity that the different hours per shift and days per week parameters yield.