This is better known as Polyphasic Sleep
Most of us are more familiar with monophasic sleep.
We sleep in one large chunk, typically at night and we’ve likely done this most of our lives.
On the other hand, polyphasic sleep involves short bursts of sleep. Taking long-ish naps multiple times in the day rather than sleeping at night in one stint. If you nail polyphasic sleep, it could definitely provide several benefits including more time, sharpened focus and longer days. Most polyphasic sleepers aim anywhere from 4-6 hours of sleep broken up throughout the day. But if you’re aiming for 4 hours, you would likely try taking 2 naps for 2 hours in the day. You could also sleep for around 3 hours at night and break into a few 20 minute naps during the day.
The most important thing to note, is that this technique will not work for everyone and it’s not overly encouraged. While attaining deep sleep is more about the quality than quantity, there are still other factors, besides just time, that inhibit our sleep.
The only way we can truly feel the benefits of deep sleep in 4 hours, is if we set up a life conducive for quality sleep.