Since the beginning of the digital age, there have been critical voices claiming that spending time with digital media might reduce time dedicated to school-related obligations, leading to detrimental effects on academic performance. However, findings on this topic are mixed and lack large-scale time-use data that allow the investigation of displacement effects from a long-term perspective. To address this research gap, we tested a Time-allocation Model of Media Use among 12- to 18-year-old students from three different media generations (Gen X, Gen Y, Gen Z). The analysis relies on high-quality daily diary data (i.e., all existing data sets of the German Time-Use Survey) collected between 1991 and 2013 (N1991/1992 = 1,310, N2001/2002 = 1,329, N2012/2013 = 1,274). The findings of the partial least squares structural equation modeling multigroup analysis demonstrate that free time availability is an important predictor of media choice. Moreover, although digital media use considerably increased over time, the effects on school-related obligation time remained largely stable and, most importantly, small. The study offers new insights into changes in media use and their effects on school-related obligation time across different generations from both a theoretical and empirical perspective. It is adaptable for future research, analyzing prospective media generations.