Effective as of July 1, 2018, South Korea set a new cap on employees’ weekly working hours, decreasing the maximum number from 68 to 52. In this study, we comprehensively analyze the effectiveness of the law’s implementation by observing changes in work time, health status, health care utilization, health behavior, monthly expenses, and satisfaction between pre- and post-implementation periods (2014–2017 vs. 2019). We find evidence of both intended and unintended consequences—and, in this last category, some are beneficial and some not. As intended, employees eligible for the 52-hour work week saw their average working hours decrease, while their monthly spending on leisure increased substantially. A beneficial unintended consequence was that work time also decreased in firms with less than 300 employees that had not yet implemented the 52-hour work schedule (they have done so since, in January 2020). Among adverse unintended consequences, the most notable were heterogeneous effects across employment types (full-time vs. precarious employment) and, in particular, negative impacts on precarious employees (that is, those facing relatively high levels of job insecurity). Despite almost no change in their work time, precarious employees saw substantial increases in outpatient visits and monthly expenses for health care, indicating suggestive evidence of adverse health consequences. Another adverse unintended consequence was that overall job satisfaction decreased among several groups of employees. This may reflect a heavy workload among employees still expected to work overtime, especially experienced employees or those working in large firms. While employment rates increased after the new schedule’s implementation, the majority were in precarious jobs. This has negative implications because of the adverse health impacts of being in precarious employment; also, the workload of experienced employees in this field might have intensified amid all the new hiring. Our findings suggest key policy recommendations for how to leverage the benefits of the 52-hour cap on weekly working hours while addressing its negative unintended consequences.