In the context of global concerns about teacher workload and the relationship between workload and attrition, understanding the nature, quantity and intensity of teachers' work is an essential first step in formulating robust solutions to this significant problem. Understanding teachers' work, however, is a complex undertaking, and prior attempts have largely been focused on the quantity rather than the intensity or quality of work required and undertaken. This article reports on a pilot study of the Teacher Time Use app, a bespoke tool developed by the research team to 'get inside' teachers' subjective experience of time through a focus on both workload and intensity. Our analysis shows that the app provides a simple, non-demanding way for teachers to record their work in a timely and efficient way. It also highlights the capacity of this approach to understand both the range and quantum of tasks that comprise teachers' work and consequently the nature and subjective experience of work intensification. We argue the need for a more nuanced empirical understanding of the layering and multi-tasking of teachers' work that characterises work intensity, and suggest that the Teachers' Time Use app provides an effective means for recording and representing the complex dimensions of teachers' work and time use.