A nap can be a beautiful thing, or it can leave you feeling hollowed out. The difference is usually just a few minutes.
Most people nap for too long. They fall into deep sleep, their alarm goes off in the middle of it, and they wake up feeling worse than before. This is called sleep inertia, and it can last up to 30 minutes. Not ideal if you were napping to be sharp for a 2pm meeting.
The 20-minute nap is the most studied and most consistently effective. It is short enough that you stay in the lighter stages of sleep, long enough that your brain gets meaningful restoration. Mood, alertness, reaction time, and even creativity all improve from a well-timed 20 minutes.
If you have more time, the 90-minute nap is the next best option. You complete an entire cycle, which means your body cycles through to the end naturally and you rise at a point that feels right. The 60-minute nap is the trickiest because it often lands you inside a period of deep sleep right as the alarm fires.
Between 1pm and 3pm is your natural dip. Your core body temperature drops slightly after lunch, your alertness dips with it, and a nap at this point works with your biology rather than against it. Napping after 4pm risks interfering with your night sleep, especially if you tend to lie awake.
Even a short nap at the right time can lift your afternoon in a way that a third coffee simply cannot. Let yourself rest.