The afternoon nap, around 20 minutes, no longer than thirty.
It's been shown to enhance productivity and creativity, reduce fatigue and improve employee wellbeing. The Japanese take their napping seriously.
Most of us tend to experience an energy slump mid afternoon which may also affect mood and decision making, a nap may help.
Having a short nap will not interfere with a good night's sleep, which is around 7-8 hours for most but not all, some of us require more, but usually not less.
For best results, if you tolerate coffee well, have cup before your nap. It takes about 7 minutes to fall asleep, the caffeine takes about 20 minutes to take effect which is about time to wake up. The cup of coffee will help you wake feeling even more refreshed and alert, ready to take on the rest of the day.