Hi, i had (and i continue have) the same kind of questions as you, about the time-concept.
To properly answer your questions, man should read --- and understand --- a lot, a lot, ..., a lot of books.
I will try to answer, some of them, taking in account i can be wrong, but exposing different points of view, i think can help.
The concept of "time rate" is a key-point to understand what really time is.
Naturally, we must assume the validity of the General Theory of Relativity of Albert Einstein. It is approved and verified by multiple experiments.
To get a "value" of "time rate" we must make at least 2 measures, that is:
O1 ---> O2 AND O2 ---> O1
O1 and O2 are both "Observers", i.e., systems capable to process information.
Say t_1_2 the time measured by O1 for O2.
Say t_2_1 the time measured by O2 for O1.
Can you find -- mathematically -- a "time" t, such that t / t_1_2 = t / t_2_1, meaning t / t1 the "time" t modulo t1, and t / t2 the "time" t modulo t2 ?
Furthermore, (have) had that question a "physical" meaning, or it is only a mathematical abstraction?
That is, why t / t =1. My answer, it is algebra.
