Up to 4 weeks can be set up with a different number of working days per week as a standard.  For example, you may wish to set up 2 weeks where one week works 8 hours a day, 5 days a week from Monday to Friday and the second week works 10 hours a day, 4 days a week from Monday to Thursday. 

To setup variable work weeks, use Resource Options & User Fields to set the number of variable work weeks and Schedule Options to set the Manufacturing week 1 date (the base date to measure what the current work week is).