Exploratory analyses
To account for the possibility of gradual improvement of the sleep parameters after the intervention, we conducted piecewise growth models. Specifically, two variables were created to code the number of the study days. The first variable (time to intervention) counted the number of days to the first night after the intervention. The first day was coded as −7, with increments of one for each study day until day 8 (the night after the intervention); all days in the second week were coded as 0 for this variable. The second time-variable (time since intervention) was coded as zero for the first 8 days, with 1 on day 9, and counted up until +6 on day 14. These two time-variables and the interaction of these time-variables with group were entered in addition to the predictors in the model above. This model allows to estimate (a) gradual changes in sleep parameters before the intervention (and differences in this change between groups), (b) gradual changes in sleep parameters after the intervention (and differences in this change between groups), and (c) an abrupt change from day 7 to 8 (and differences in this change between groups). None of the change parameters or the interaction of change parameters with group were statistically significant, In an additional model, we examined change in the sleep parameters combined across the two groups. To that end, we re-estimated the pricewise growth models above, but removed the group variables (In further exploratory analyses, we examined if there was evidence for an intervention effect on subjective stress. Using subjective stress as the dependent variable in the same models (Lastly, in further non-pre registered analyses, we examined if the two groups differed in the CAR from before to after the intervention. We examined intervention effects by predicting CAR from study week, group, and the group*week interaction in a multilevel model. As covariates on the between-person level, we included gender, intake of hormonal contraceptives, age, and body mass index. On the within-person level, we included consumption of drinks and the average activity level reported during the CAR assessment period. The main effects of group, 