The reason many tech companies fail is not a bad product/market fit, the wrong technological approach, or lack of experienced CFO, but the design — not just the website UX but the design in its entirety. The way things are integrated together. The creative process.
There is no rule. The general consensus is that you can close your eyes and relax for about a half-hour at the most. It is important not to fall into a deep slumber, and that can leave you feeling groggy. Set the alarm for your snooze. However, some experts are of the opinion that 90 minutes is the ideal time because the body gets sufficient time to complete one sleep cycle. Doze for 90 minutes, and you wake up refreshed, and it also boosts creativity.

Take a nap to wake up refreshed
Understood about Stage of Sleep will help you know the suitable hour you spend for a nap.

Why this is ideal can be best understood by knowing about stages of sleep.

Stage one is when sleep sets in and the brain generates alpha and theta waves. This stage lasts seven minutes, and when you wake up, you have just had a catnap.

During stage two the brain wave frequency increases and slows down. Wake up after stage two, and it is best because you feel refreshed.

The third and fourth stages are deep sleep during which the brain produces slower delta waves, and it is difficult to wake up. If you do, you feel lethargic.

REM sleep occurs 90 minutes after falling asleep, and there can be several cycles during the night. You dream.

(sleepsherpa.com)