Although quarantine is an effective measure for containing the spread of COVID-19 and reducing the number of infected individuals, it has had negative consequences on the emotional well-being and academic performance of university students. To explore the influence mechanism of school quarantine time on academic procrastination among students, a survey research methodology was employed to assess quarantine time, negative affect, ego depletion, and academic procrastination among 538 Chinese university students, and the Statistical Package for the Social Sciences software suite was used to analyze the collected data. The results indicated that (1) there were significant positive correlations between school quarantine time and academic procrastination, (2) school quarantine time had no direct effect on academic procrastination, but it positively predicted negative affect and ego depletion, and (3) school quarantine time affected the levels of academic procrastination among university students through three indirect paths: the mediating role of negative affect, the mediating role of ego depletion, and the chain mediating role of both negative affect and ego depletion. This cross-sectional study concludes that negative affect and ego depletion could mediate the association between school quarantine time and academic procrastination among university students during the COVID-19 pandemic.