The planned hours on monthly basis can be set up via the page "Planned hours" of the respective co-worker. If the default planned hours of the company were previously activated for this co-worker, this has to be deactivated first. Afterwards, you can edit the existing planned hours or add new ones. Here, it is possibl now to change the working time type from "weekly" to "monthly" and define a monthly target, as well as the weekly working days.
In the next step, the holiday quota of the employee should be adjusted manually according to the number of fixed work days.