The aim of this study was to investigate time use in work/education, self-care/self-maintenance, play/leisure, rest/relaxation, and sleep in people with persistent mental illness. A further aim was to investigate how time use in the daily activities was associated with health-related variables and social interaction. The study comprised 103 participants with a diagnosis of persistent mental illness who completed self-ratings and interviews in order to assess (1) time use of activities during one 24-hour day, (2) social interaction and (3) health-related factors. The major results indicated that the total time in activity (TTA) and the time spent on work/education and sleep seemed to be related to the majority of the target variables. Four groups of daily rhythm were identified and the daily rhythm groups differed concerning perceived mastery and social interaction. Although the results of this study were statistically significant they did not indicate clinical significance. Therefore, the assumption that there is a relationship between occupation and well-being could not be clearly verified. This study had a cross-sectional design based on a one-time measure, which is an important limitation for the validity of the study. Furthermore, no Bonferroni corrections were made for mass significance and some of the findings would have disappeared if such corrections had been made. More studies concerning time use in daily activities, and daily rhythm in relation to health and well-being are needed.