The 24-hour Society undergoes an ineluctable process towards a social organisation where time constraints are no more restricting human life. The borders between working and social times are no more fixed and rigidly determined, and the value of working time changes according to the different economic and social effects you may consider. Shift and night work, irregular and flexible working hours, together with new technologies, are the milestone of this epochal passage. What are the advantages and disadvantages for the individual, the companies, and the society? What is the cost/benefit ratio in terms of health and social well-being? Coping properly with this process means avoiding a passive acceptance of it with consequent maladjustments at both individual and social level, but adopting effective preventive and compensative strategies aimed at building up a more sustainable society. Flexible working times now appear to be one of the best ways to cope with the demands of the modern life, but there are different points of view about labour and temporal 'flexibility" between employers and employees. For the former it means a prompt adaptation to market demands and technological innovations; for the latter it is a way to improve working and social life, by decreasing work constraints and increasing control and autonomy. Although it can be easily speculated that individual-based 'flexibility" should improve health and well-being, and especially satisfaction, whereas company-based flexibility" might interfere negatively, the effective consequences on health and well-being have still to be analysed properly.