Idle time is a period at work when employees cannot complete their work tasks for reasons beyond their control. Combining action regulation theory and the job demand–resource model, we propose that idle time is a regulation requirement that necessitates employees to adjust their behavior, which bears both risks and opportunities. We propose that the direction of relations between idle time and occupational well-being outcomes, namely, exhaustion and engagement, depends on the context and the way employees use idle time. The relation between idle time and well-being is likely to be positive when work overload or autonomy is high or when idle time is accompanied by recovery experiences of relaxation or detachment. By contrast, the relation should be negative when overload, autonomy, and recovery experiences are low. Differentiating between idle time as a temporary (within person) and a chronic (between person) regulation requirement, we tested our hypotheses in a sample of 1,036 participants in a five-wave longitudinal study. Results of mixed modeling showed that, within persons, the relation between idle time and exhaustion was positive in periods when autonomy was lower and negative when autonomy was higher. Between persons, this relation was positive for employees with higher overload and negative for those with lower overload. Both within and between persons, the negative relation between idle time and engagement was stronger when autonomy was higher. Detachment during idle time was associated with higher exhaustion, but not with engagement, whereas relaxation during idle time was associated with lower exhaustion and higher engagement.