This study examines the opportunity cost of non-research responsibilities on research output. Using a sample of early career faculty members who received their Ph.D. in economics, we consider the effect of two dimensions of time use on research output: (1) time allocation, or how time is divided between research and other duties and (2) time concentration, or how research time is distributed during the academic year relative to summer months. This second dimension has not been used in prior studies on research productivity; however, the inherent delays in the publication process as well as start-up costs may imply that concentrating research time exclusively in the summer months reduces research output. We find that both dimensions of time use are significant predictors of peer-reviewed publications and that time concentration is a significant predictor of submissions. We find gender differences in both dimensions of time use, which are attributable to gender differences in employment at research institutions and on-going childcare responsibilities.