We already know that moral decisions are shaped by your mood. A new study suggests that the time of the day similarly affects decisions of a moral nature.
Maryam Kouchaki of Harvard University and Isaac H. Smith of the University of Utah found a clear connection between the decisions you make and when you make them:
The normal, unremarkable experiences associated with everyday living can deplete one's capacity to resist moral temptations. In a series of four experiments, both undergraduate students and a sample of U.S. adults engaged in less unethical behaviour (e.g., less lying and cheating) on tasks performed in the morning than on the same tasks performed in the afternoon. This morning morality effect was mediated by decreases in moral awareness and self-control in the afternoon.
In short, if you are relying on someone to make a decision that requires a sense of fair play, it's best to ask them about it in the morning rather than later in the day. If you are the decision maker, be fair and think it over when you wake up.