I have no idea how the concept of time developed among primitive man, but it is definitely clear that today we are very aware of the concept of time; and in fact, have broken down the passage of time way beyond the concept of days. Today, we have broken the passage of time into hours, minutes, seconds and even fractions of seconds. This allows us to calculate many aspects of speed and physical performance, but also allows us to reflect on how we spend the 24 hours that encompass a whole day, which is the amount of time it takes our planet earth to complete one full rotation.
With this knowledge it is also possible for us to deduce how much of our lifetime is spent asleep. If we sleep eight hours a day, then we know that a third of our life is spent in the sleeping mode. This may seem like a lot, but it should be noted that any attempt to shorten this ratio usually results in catastrophic results for the person involved. With this in mind it is always good advice to get a “good nights’ sleep” no matter where you are.