This paper examines the effects of working time regulations on the allocation of workers and hours. I exploit a unique reform introducing a minimum workweek of 24 hours in France in 2014, affecting 15% of jobs. Drawing on administrative data and an event study design, I find a firm-level reduction in total hours worked, showing imperfect substitutability between workers and hours. The effects differ by gender: women working part-time were replaced by men working longer hours. Importantly, workers also reallocate between firms. To quantify the aggregate impact accounting for these effects, I build and estimate a search and matching model with firm and worker heterogeneity. Overall, the minimum workweek reduced employment by 1.4%, largely driven by women, and decreased total hours by 0.5%.