Intuitively, we can think time as the number line, and divide it into intervals whose length are all same; the unit chosen can be an year, month, day, hour, minute, second, and so on. Then, we can order the intervals and put numbers on them in a particular way, and we call the label a date. For examples, on a yearly basis, 2026, 2027, and so on, or on a monthly basis, May 2026, June 2026, and so on.
We can evaluate the length of any interval on time. It can be expressed in particular units. For examples, on a yearly basis, 2 years, 3 years, etc., or on a monthly basis, 3 months, 1 year and 2 months, etc.
In everyday life, we would say “the meeting is on May 21, 2026.” When we write the time interval which the order indicate as $I$, the content to which that utterance mostly corresponds can be expressed as “$\text{the meeting start time}\in I.$” We don’t specify as the exact time but suggest the neighborhood which it belongs to.
Since we use approximated time, time intervals’ lengths are bound to be approximated in consequence. We can calculate the elapsed time between to events like this:
\[\begin{aligned} \text{event}_1\in I_1, \text{event}_2\in I_2 \ \ \text{where their order is respectively } O_1, O_2 \\ \Rightarrow \text{the time elapsed}\in (O_2-O_1-1, O_2-O_1). \end{aligned}\]For an example, from the fact that Albert Einstein was born in 1879 and dead in 1955, we can determine his age as follows: $\text{the exact age}\in (75, 76).$ One way to explain this result is to think that a date also represents the start point of the time interval.