What are custom workdays?
Does your work week start on Sunday and end on Thursday? Do you work on Mondays but not on Tuesdays?
If so, you can do the following:
Customize the time period on a widget to start your week on a different day than Monday,
Create a formula in the Advanced formula editor that allows you to define custom workdays (for example, only Mondays, Wednesdays and Thursdays).