The quantum of instruction time allocated to curriculum subjects such as mathematics facilitates greater exposure to knowledge and skill development, leading to higher levels of achievement. There are a number of manifestations of time to consider when investigating the quantum of time in mathematics education. The OECD have investigated the time allocated to mathematics by schools internationally, while also reporting on the prevalence of private tuition and time spent on homework. However, to date, no attention has been afforded to the provision of 'hidden curriculum time' for mathematics. This study seeks to advance the work of the OECD and describes a case study that sought to ascertain if teachers in Ireland provide additional mathematics lessons outside of school hours. The authors examined how prevalent this practice is, how many additional minutes some students receive as a result of this practice and ascertained teachers' reasons for providing/not providing these additional mathematics classes. The results from this case study show that the majority of teachers at Senior Cycle provide these classes while a large proportion of Junior Cycle teachers also do. In extreme cases, these additional classes expose students to an additional 88.3 h of mathematics over the two-year Senior Cycle programme.