Using nationally representative data from Australia, the paper examines the relationship between time of day and cognitive performance among working-age individuals. We show that performance on cognitive tests involving fluid intelligence peaks in the afternoon, with poorer performance in the morning and evening. This time-of-day effect is most pronounced in the early afternoon and stronger for women than for men. However, there is no such evidence on an empirical link between time of day and crystallized intelligence. Overall, we show that the U-shaped profile of cognitive performance over the course of the day found in Gaggero, A., and D. Tommasi. (2023. "Time of Day and High-Stake Cognitive Assessments."Economic Journal 133: 1407-29) for university students can be generalized to people of working age.