The 8 hours single sleep phase during night appears to be kind of artificial and not what humans are supposed to do. Why, you ask? Well, before artificial light sources became widespread people went to bed after sunset and slept for a couple of hours, woke up in the middle of the night, did some stuff (that time was in fact often used for reproduction purposes) and slept a couple of hours more until sunrise.
Another example are babies. They don't just sleep during the night but nap during the day for shorter periods of time.
In countries with high temperature during the day people often sleep mid day and call it siesta.
Military and medicinical personell sometimes need to adapt their sleep cycles to their work, so they go for two days without sleep and sleep for a whole day afterwards.

After all those examples, why do you still stick to the normie sleep during night method? Polyphasic sleeping is told to have been used by many scientists of the past and while there unfortunately aren't any long term studies of its consequences there is anecdotal evidence that it makes at least some people more efficient.