With the prolongation of non-ordinary situations such as school closures due to the coronavirus disease 2019 (COVID-19) pandemic, high school students have experienced irregular sleep-wake cycles and elevated academic stress resulting from reduced academic achievement and widened gaps in academic performance. This cross-sectional study aimed to investigate the associations among chronotype, social jetlag, lifelong learning competency, and academic stress in high school students during the COVID-19 pandemic. Data were collected through an online survey from May-June 2021. The mean social jetlag was found to be 2 h and 9 min, and multiple regression analysis revealed that social jetlag and lifelong competency affected academic stress. Thus, measures to minimize social jetlag and improve lifelong learning competencies should be implemented to reduce academic stress among high school students. School nurses should identify students with severe social jetlag and provide guidance and interventions to promote sleep hygiene and regular lifestyles.