What Drives Girlfriends' Bedtimes? Experimental Effects of Social Technology Use and the Role of Friendship and Personality

Technology use is often implicated in adolescent sleep difficulties, yet experimental evidence confirming its impact on bedtime is critically lacking. This study tested whether online socialising with friends delays bedtime compared to non-social online media use, while also considering the roles of friendship quality and personality. Seventeen pairs of female friends (N = 34; ages 16-18 years) spent two nights in a sleep laboratory: one night online socialising with their friend in another room (WhatsApp + Netflix), and one night watching Netflix alone without socialising. Condition order was counterbalanced across pairs. Bedtime was behaviorally observed using infrared cameras. The following morning, participants reported who initiated sleep and their reasons for going to bed. They also completed questionnaires on friendship quality, co-rumination, self-control, bedtime procrastination, and a sleep diary. Multilevel models accounted for the nested structure of repeated assessments within individuals within dyads. On average, participants went to bed later during online socialising than during non-social online use, although this difference was not statistically significant. However, higher friendship quality significantly predicted longer bedtime delays during online socialising, with delays up to 72 min. Feeling sleepy was the primary reason for sleep onset, rather than social motivations. Additionally, there were clear associations between self-reported sleep initiation and bedtime procrastination and behavioural observations of earlier and later bedtimes, respectively. These experimental findings suggest that online socialising may delay adolescent bedtimes, particularly among those with high-quality friendships. These results underscore the importance of addressing peer dynamics and individual differences in supporting healthy adolescent sleep.