From The Screwtape Letters—a fictional work written from a senior demon’s perspective, advising a junior tempter.

In the first place I have always found that the trough periods of the human undulation provide excellent opportunity for all sensual temptations, particularly those of sex. This may surprise you, because, of course, there is more physical energy, and therefore more potential appetite, at the peak periods;

The Screwtape Letters
C. S. Lewis