Time-out (TO) is a widely utilised parental discipline technique with a strong evidence-base that nonetheless has attracted controversy regarding potential adverse effects on mental health in developing children. Associations between TO implementation and mental health outcomes have rarely been investigated, especially through the eyes of children who grew up experiencing TO. This study recruited 407 university students (Study 1) and a community sample of 535 young adults (Study 2); both samples aged 18–30 years. Young adults were surveyed on their retrospective reports of childhood TO experience, childhood experiences of adversity, perceived parenting style and parental attachment, and their current mental health outcomes (attachment style, emotion regulation and mental health). In Study 1, 334 (82.1%) young adults reported experiencing TO in childhood, but with widely varied implementation that differed considerably from its evidence-based ideal. Reports of more TO appropriate implementation were associated with less avoidant attachment, better mental health, and emotion regulation, over and above the effects associated with authoritative parenting and secure attachment in childhood. While exposure to childhood adversity was associated with poorer adulthood outcomes, TO implementation did not moderate the association. Study 2 replicated most findings from Study 1, except that appropriate TO implementation displayed a positive association with mental health and no associations with anxious and avoidant attachment and emotion regulation. These findings suggest the safety of TO use with young children, including those who experienced childhood adversity, and highlight the importance of disseminating sufficient parenting information on TO in the community.