Many previous time allocation studies treat work as a single activity and examine trade-offs between work and other activities. This paper investigates the at-work allocation of time among teaching, research, grant writing and service by science and engineering faculty at top US research universities. We focus on the relationship between tenure (and promotion) and time allocation, and we find that tenure and promotion do affect the allocation of time. The specific trade-offs are related to particular career paths. For example, full professors spend increasing time on service at the expense of teaching and research while longer-term associate professors who have not been promoted to full professor spend significantly more time teaching at the expense of research time. Finally, our results suggest that women, on average, allocate more hours to university service and less time to research than do men. (Contains 1 figure and 8 tables.)