The COVID-19 pandemic in 2020 has threatened people’s health and drastically changed their lifestyles. An international collaborative study, Time Social Distancing (TSD), was launched to investigate the effects of the COVID-19 lockdown on time perception and psychological states. The present study obtained longitudinal data from 108 Japanese people in their 20s to 60s over three sessions to investigate how people’s loneliness, anxiety, and sleep hygiene changed during confinement, and whether age affected these changes. The sessions took place during the confinement, ten days after the confinement, and four months after the confinement. The latent curve models showed that loneliness gradually increased throughout the experiment, while anxiety decreased. Sleep quality and chronotype did not change over time. The baseline of loneliness and anxiety/depression decreased with age, and there was a slight tendency to become more morning-oriented. The effect of age on sleep quality was not confirmed. Autoregressive cross-lag modeling suggested that the interaction between chronotype and the other three variables was small and the changes of loneliness and sleep quality may precede that of anxiety.
