In the morning, we start off feeling fresh and rested (ideally, at least). As the day wears on, sustained cognitive engagement depletes our mental resources, and our behavior changes for the worse.

Every day we make decisions that have important implications for our happiness and how we live our lives. Whether we are studying for an exam, preparing for a job interview, or deciding on the best outfit for a first blind date, these very different situations have something in common: They happen at a certain time of day, a time we often can choose or control.

When making decisions, we often don’t consider how the time of day might affect our choices. Rather, we decide on a time based on what’s most convenient to us. Yet recent research suggests that time of day has an important effect on our behavior and the actions of others.

In addition, time of day influences how we interact with others. In recent research (not yet published), Maryam Kouchaki (of Northwestern’s Kellogg School of Management), Dan Cable (of the London Business School), and I reviewed field data from the MBA admissions office of a top U.S. business school. Somewhat shockingly, we found that time of day influences admissions officers’ evaluations of applicants as much as their educational background and work experience. Specifically, applicants were evaluated worse later in the day because interviewers conducted less structured interviews as the day wore on. Interestingly, neither students nor admission officers were aware of the relevance of such time-of-day effects.

We know that fatigue tends to accumulate over the day, but we generally fail to consider that our performance suffers as a result. Add to that the fact that we often feel concerned about being as productive as we can and thus often turn opportunities for a break into additional work (e.g., eating lunch at our desk). We can do better by taking breaks, and by carefully choosing the time of that appointment, interview, or date.