Using the personal correspondence of young people in detention, this article explores different meanings of time in Belgian reform schools between 1900 and 1960. The first section examines how youngsters and their families conceptualised time and age in petitions for release. With the establishment of the Children’s Court in 1912, the length of confinement in a reform school was not decided during the trial, but became dependent on the minor’s behaviour during the re-education process. This influenced how youngsters and their families framed their requests for release. Next, I analyse how juveniles experienced time during their confinement. The strict regulation of time is inherent to disciplinary institutions, defined by detailed timetables and influenced by both calendar time and seasonal time. Many juveniles defined the passing of time as a countdown towards the day of release. Lastly, I explore how social and historical views on youth influenced the juveniles’ detention experience and how they used their youthful age, as opposed to childhood, as an argument to negotiate changes to the reformatory conditions. Overall, this article contributes to our understandings of juveniles’ experiences of time during confinement, their views on age and how the two were intertwined.