Working hours are generally fixed by collective agreement. Working hours are presently 37 hours a week on average (full-time employment).
It is possible to obtain an agreement on part-time employment, but this will depend on the local planning and organization of work, and the decision lies with your head of department/executive head.
Employees who plan their own work, or whose working time cannot be checked are not entitled to overtime pay. However, the employer may grant overtime remuneration by specific assessment if the scope of the additional work has been considerable.