Employees face many temptations to behave unethically at work. Resisting those temptations requires energy and effort. But the energy that is essential to exert self-control waxes and wanes. And when that energy is low, people are more likely to behave unethically. This opens up the possibility that even within the same day, a given person could be ethical at one point in time and unethical at another point in time.

Over the past few years, management and psychology research has uncovered something interesting: both energy and ethics vary over time. In contrast to the assumption that good people typically do good things, and bad people do bad things, there is mounting evidence that good people can be unethical and bad people can be ethical, depending on the pressures of the moment. For example, people who didn’t sleep well the previous night can often act unethically, even if they aren’t unethical people.

Our research started from this idea. Drawing from recent research indicating that people can become more unethical as the day wears on, we asked whether this plays out the same way for people who show different patterns of energy during the course of a day. Fatigue researchers have discovered that alertness and energy follow a predictable daily cycle that is aligned with the circadian process. However, different people may be shifted in their circadian rhythms. Some people are “larks” or “morning people” in that their circadian rhythm is shifted earlier in the day. They are most easily detected by their natural tendency to wake early in the morning. Others are “owls” or “evening people” and they are shifted in the opposite direction. Larks tend to get up early, and owls tend to stay up late.

Building from this research, we predicted that larks and owls would follow different patterns of ethical and unethical behavior over the course of a day. Because their energy levels should follow different patterns, and this energy is crucial for resisting temptation, we expected larks to be more unethical late at night than early in the morning, and owls to be more unethical early in the morning than late at night. To test this prediction, we conducted two laboratory studies.

In our first study, we focused only on behavior in the morning. We brought research participants into a laboratory, and gave them a simple matrix task in which we paid them additional money for each additional matrix that they said they solved. Participants believed that their work was anonymous, and could thus over-report to earn more money. But we were able to go back and determine how many they actually solved. In other words, we could determine who cheated by over-reporting the number of solved matrices. Consistent with our prediction, since these were morning sessions: night owls were more likely to cheat than larks.

In our second study, we tested the full prediction—that unethical behavior would depend on both circadian rhythms and the time of day. We randomly assigned a new set of research participants to a laboratory session either early in the morning (7-8:30am) or late at night (midnight-1:30am). Participants undertook a die rolling task previously established as a test for unethical behavior. In this task, they anonymously rolled a die and reported the number back to us, and we paid paying them based on the number they reported (higher amounts for higher rolls).

Although we didn’t know what numbers participants actually rolled, we did know that everyone should report an average of 3.5. So any systematic differences across conditions (morning people in the morning vs. evening people in the morning, for example), would indicate cheating. Consistent with our prediction, an interesting and statistically significant pattern emerged. Larks in the night session reported getting higher rolls (M=4.55) than larks in the morning sessions (M=3.86), and owls in the morning session reported higher rolls (M=4.23) than owls in the night sessions (3.80). This evidence is consistent with the idea that larks will be more unethical at night than in the morning, and that owls will be more unethical in the morning than at night. A more detailed description will be provided later this year in our forthcoming article in the journal Psychological Science.

The important organizational takeaway from these findings is that individual may be more likely to act unethically when they are “mismatched” -that is, making a decision at the wrong time of day for their own chronotype. Managers should try to learn the chronotype (lark, owl, or in between) of their subordinates and make sure to respect it when deciding how to structure their work. Managers who ask a lark to make ethics-testing decisions at night, or an owl to make such decisions in the morning, run the risk of encouraging rather than discouraging unethical behavior.

Similarly, people who control their own work schedules should structure their work with their chronotype in mind. Many of us are tempted to squeeze in that extra hour of work. If we’re a morning person squeezing it in at night, though, we create a situation in which resisting temptation may be harder than ever. Owls who schedule extra hours for themselves early in the morning face the same issue.