The interest in 8-hour and 12-hour shifts is not entirely recent; however, it earns an emergent status on the research hypotheses due to a conjuncture that leads more workers into such schedules, as well as due to the existence of evidence about their negative consequences on the workers’ health. Based on the analysis of the change from an 8-hour to a 12-hour schedule in a Portuguese company, this study aims at discussing the factors and conditions considered as aggravated risks in 12-hour days. This study brings to light a resizing of the difficulties felt by the workers, both in their health and at work. Moreover, this study points out that the way each worker (immediately and in the long term) thinks through the sustainability of a 12-hour shift brings to debate the specificities of the work content, the demands of life outside work and the stage of the professional trajectory.