The Russian proverb, morning is wiser than evening (MWTE) is one of my favorite ideas about tempo management at the daily level. It makes a more abstract idea (avoid making decisions when you are tired or depressed) more evocative.
MWTE is a simple tempo management heuristic that works for most people, most of the time. If you are a typical sort, and you use it systematically, you’ll slightly improve your decision-making quality by introducing a timing bias. Most of the time. Sometimes, you are smarter at night-time. And there are people who are always wiser in the evening. Good heuristics have this robustness. Even if you proselytize them with no qualifications, on balance you’ll do more good than harm. Really robust heuristics can even handle being rhetorically exaggerated into absolutes (“If you practice MWTE, you will succeed, guaranteed!”). They are also very forgiving: if you execute partially, you get partial results. There is no all-or-nothing effect.
The 24-hour circadian rhythm is usually the easiest one to work with when you first start to practice tempo management. This is the reason take it one day at a time is such a robust heuristic for tough times. The world of motivational speakers and self-improvement gurus is choked with circadian advice. It is useful to sort out the torrent of circadian tips this world throws at us. A decent classification is good, bad and ugly heuristics. It is the last category that determines the quality of your daily life.