Phi-Bi

If you have a relatively constant wake up time, then you can push your sleep duration to 5 hours. This schedule does help in keeping fresh, but in my experience only works for 5-6 days in a week. There'll be 1-2 days where you'll just collapse and fall asleep for 7-8 hours. However, it is possible to sustain this for months. If feeling a bit drowsy, 5-10 minute of nap does restore freshness.

If you're a bit adventurous, you may attempt the following

Leonardo da Vinci's sleep schedule included 20-minute naps every four hours. Da Vinci followed an extreme form of a polyphasic sleep schedule called the Uberman sleep cycle, which consists of 20-minute naps every four hours.

In my experience, sleeping 5-6 hours will only result in more napping.