The unpredictability of working time is a seldom studied, but increasingly prominent, feature of employment across occupations, including those where nonstandard or unsocial hours have become the norm. This paper proposes that unpredictability which is driven by employer demands for flexibility (e.g. scheduling practices) is associated with greater employee work-life conflict and perceived stress. This, in turn, has implications for health behaviour (alcohol consumption, sleep disturbance) and symptoms (digestive and cardiovascular problems). Increasing employee control through flexible working arrangements is examined as a potential moderator. We also examine the possibility that alcohol consumption exacerbates the negative effects of unpredictability on wellbeing and health. A survey of 1207 police officers, for whom working unsocial hours is commonly accepted, showed direct effects of unpredictability over and above nonstandard hours on digestive health, and indirect effects through wellbeing on sleep, digestive and cardiovascular health. In some cases, these indirect effects were reduced or absent with greater employee control through flexible working arrangements, although this was not uniform. The interaction of alcohol consumption was found to intensify the negative effects of unpredictability on wellbeing and some health outcomes. The findings reflect a tension between employer-centred strategies for enhancing workforce flexibility and flexibility practices which purport to provide employees with greater control and work-life balance. They are consistent with wider increasing strategic pressures towards employer-centred flexibility and suggest a challenge for sustaining employee wellbeing as working time becomes more unpredictable.