The archaeological context of a recently unearthed sundial from the Egyptian Valley of the Kings suggests that the object was used to define the work hours of labourers engaged in building tombs. An analysis of the sundial enables us to establish its precision and the scientific rationale on which the measurement of time is based. This allows us to gain insights into the role of astronomical time in Egypt c. 1200 BC. Administrative texts of the same period found nearby offer additional evidence on the everyday life of the workmen and the importance of social time in regulating their activities. This provides us with a unique opportunity to compare astronomical with social time and ponder the arising implications from the convergence or divergence of the two.