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Referring back to the Unix’s timeline (you can read about Unix time in our previous post here), any point along the line would be called an instant in time.

An instant in time does not tell you a date, a year or anything. It just tells you a number, which is the amount of measurement seconds/milliseconds from the epoch to that instant.

Let’s take 00:00 a.m of 30th of August 1990 on the timeline above; in Unix time, it would be represented as 651974400. Which is how many milliseconds from the epoch to the current instant. We can do a lot of things to represent the number as a date. However, if you want to get down to the basics, it’s just an instant in time.

The timeline shows different reprensentations of what is known as instances in time

A duration of time is the time that covers the span between one instant in time and another. It has the same characteristic as instant time, which doesn’t say anything about date. What we get is the numbers of milliseconds passed from one instant in time, to another. In order to convert Unix time into date, we therefore calculate the date by counting forwards from epoch in milliseconds, to the instant that the UNIX timestamp expresses. Therefore, date and time can be two very different thing using the Unix system.