<p>This review examines emerging evidence on the relationship between behavioral sleep timing and psychiatric disorders, highlighting the critical distinction between circadian preference (chronotype) and actual timing of sleep. These two concepts are not identical and show independent and interdependent impacts on a variety of mental health outcomes. Evidence suggests that actual sleep timing, rather than chronotype preference, is a stronger predictor of mental health outcomes, with late-night sleep patterns more consistently linked to poorer mental health across both cross-sectional and longitudinal studies. The mechanisms linking late night sleep patterns to poorer mental health are not well understood and cannot be fully explained by reduced sleep duration or being awake during the biological nighttime. Modifiable social and environmental factors likely play a role. Future research should clarify causal mechanisms and inform culturally sensitive, chronobiologically-informed interventions.</p>