Some people have experimented with the idea of sleeping in two chunks instead of one long night. This idea has come about basically because many of us have lifestyles that are not conducive to sleeping nine hours a night. Also, history shows that two sleeping shifts were commonplace in some households in the past.
During the most extended sleeping, prehistoric people would visit friends, have sex, pray, and do other calming activities during the sleep break. Not much can be done, without sunlight, so nothing too active. Then after a couple of hours, they would go back to sleep until sunrise.
The main thing to understand about that past is that we did not have electricity then. Therefore night-time was longer due to not having artificial lighting. By this standard, people usually slept about ten hours a night, in two shifts of approximately five hours. Additionally, they did not have regular jobs as they do now instead, they lived off the land. Thus, their time was used differently.
This sleeping method can work for people who do not need to live in the daily schedule. It is for most people who have typical day jobs and an average nightlife. So, if you have an open daily routine, it can work for you. Aim for two five-hour shifts, which should result in at least the seven to nine hours of sleep you need every 24 hours.
The main thing to do is to figure out what works best for your lifestyle. More than likely, due to how people live today, it is easier for you to stick to a regular night-time sleeping schedule and daytime working schedule.
However, do not force it; if you try something and after a couple of months. If you are not experiencing the good health and energy you hoped, try something new. Regardless of when you sleep, getting your sleep environment right is the ultimate way to ensure you can get the quality sleep you need.