Social jetlag can negatively impact tourists’ travel experiences. However, how social jetlag influences tourists’ review-posting behavior remains unclear. Grounded in conservation of resources theory, we leverage the exogenous variation created by daylight saving time transitions to investigate whether and how social jetlag affects review helpfulness. Based on a comprehensive dataset of 922,831 reviews across 1,337 hotels in Chicago, New York, and Orlando between 2007 and 2021, we find that social jetlag significantly reduces perceived helpfulness of reviews. The information richness of reviews mediates this detrimental effect. Moreover, the negative effect is more pronounced for reviewers reporting low sleep quality. This study contributes to the literature on user online engagement by addressing the overlooked influence of temporal biological factors in shaping digital engagement in the tourism context.