Working on duty is a common practice in professional life. It is well known that employees, such as doctors, nurses, ambulance drivers, firefighters and IT workers frequently work on duty. Although the nature of on duty service varies from sector to sector, it can generally be divided into two categories. The employees can either perform their on-duty service at the workplace or at a location designated by the employer (such as a hospital, ambulance, or radio station), or they can be on-call without having to be physically present at the workplace. These can be held outside of regular working hours throughout the day (day float) or divided after regular working hours, such as 17:00-24:00 or 24:00-08:00 (night float). There has been a significant change in the Court of Appeal’s approach to working on duty, where the employee, although not being at work, immediately starts to work or responds to a call if needed. This change in approach necessitates rethinking the concept of working hours. Initially, the Court of Appeal differentiated based on whether the on-duty work was performed at the workplace or not. For on-call duties at the workplace, the Court of Appeal would calculate the working hours regardless of whether the employee was actively working (subtracting the time assumed to be used for eating and drinking and other needs). However, for on-call periods where the employee was ready to respond without being at a location designated by the employer, these periods were not counted as working hours. The Court of Appeal would consider these periods as rest time unless the worker was called to work and actually performed work, in which case the time would be counted as working hours. The Court of Appeal has recently changed its jurisprudence, ruling that a suitable portion of the on-call period should be counted and remunerated as working hours, even if the employee is not required to go to the workplace. This study, which aims to open a discussion on the concept of working hours in the light of the Court of Appeal’s current judgments, is prepared by using the comparative law method. Since German law has regulations specific to working on duty, the comparison is primarily made with German law, and the approach of the European Court of Justice is examined to discuss whether this approach can be applied in Turkish law.