This study examined the longer-term individual- and school-level changes in students 7 months after a 1-hour delay in school start time (SST). Two cohorts of grade 11 students (N = 227; 60.8% female, age = 17.0 [0.85]) at a residential high school in Hong Kong completed a questionnaire assessing sleep duration, insomnia symptoms, depression, anxiety, stress, and subjective well-being in 2017 and 2018, respectively. One of the cohorts was reassessed 7 months after the implementation of a delay in SST, from 07:30 am to 08:30 am (n = 83, 65.1% female). School-level data on breakfast consumption, attendance, tardiness, and health clinic visits were collected. Between-group and within-group prospective comparisons suggest that the delay in SST was associated with improved sleep duration, mental health, and life satisfaction. School-level data revealed increased breakfast consumption and decreased unexcused absences, tardiness, and clinic visits. Copyright © 2024 The Author(s).