How to best utilise curriculum time has long been a question for England's schools which are free to vary time between subjects, or to extend the school day/week. This question has now risen to national prominence as policy makers consider ways to help support students catch up lost learning after the COVID19 pandemic. To illuminate this issue this paper explores the relationship between instruction time on GCSE attainment and value-added scores for 2,815 English secondary schools using panel data from the 2010-2014 School Workforce Census. Robust estimates suggest that instruction time has a small effect on attainment in each of English, mathematics, science, and humanities. Based upon subgroup analysis, effects sizes are also estimated for pupils with varying prior achievement, and for those in receipt of free school meals. These too appear small, suggesting vis-a-vis instructional time, sometimes, less might be more.