Time is a constant only when objects behave with infinite speed, or infinite value of change otherwise time is a variable and with this property it holds a very unique place in space time. It is because of time that we observe changes, growth of decline or remaing the same. Time gives us to understand the universe very well.

It depend s on the context but generally the time for such physical and mathematical equations is not constant but variable.

Dear Malaoui,

If the time measuring device is part of place which is in equilibrium motionally, in this case the time measured is physically constant, in such a case have to be accepted constant mathematically too. The time will be same at others system if they are in equilibrium motionally. (corresponding to Galilean transformation).

Time is just a concept; they way you use it, either physical or mathematical depends largely on an individual.

Following

It is variable.

A mathematical relation is, a relationship between sets of numbers or sets of elements.

Often you can see relationships between variables by simply examining a mathematical equation. Many physical relationships in electrostatics, electrodynamics, thermodynamics, etc. are expressed by mathematical equations.

it is variable ...

Time depends on gravity.

Therefore, on an interplanetary scale it should be considered as variable.

In classical physics, time is typically either an independent variable or a dependent variable of an equation. Either way, a variable. The unit of time is constant, in classical physics. There is a standard second, just as there is a standard meter. But just because a unit of measurement has been standardized, it doesn't mean that this measurement is treated as a constant, in an equation.

In special relativity, time is also a variable, but is different in different frames of reference, depending on speed. So the unit of time itself can vary. (And wouldn't you believe it, even that is being debated in some circles. Some are now saying that time dilation is a huge mistake perpetrated on the innocent, only because acceleration was not considered properly in experiments.)

For the respectable people who say that time is variable, are the fundamental equations of physics variable from a planetary system to another, in this case, are the time derivatives of Ohm's law, the law of faraday, law of thermodynmics, ... ect, is variable?

Malaoui, yes, as far as can tell, physical equations work throughout the universe, if that's what you're asking. Even the standard second can be used throughout the universe, as a unit of measure, although it would not be related in any way to the rotation of any given heavenly object. But even on earth, the standard second is no longer based on the speed of rotation of the earth. Not directly.

The physical constants that are used on earth, such as the gravitational constant, will obviously not apply to other heavenly objects, unless they happen to have the same mass as earth. But that's to be expected. Any constant which depends on the earth's specific environment will most likely be different somewhere else.

For example, when looking through telescopes at distant stars or galaxies, we compute the age of that image based on how long it takes for light to travel from the object to the telescope on earth. Our use of the standard second applies throughout the universe that we can see, and the speed of light through a vacuum, c, applies just as well here as it does everywhere else.

Time is a constant only when objects behave with infinite speed, or infinite value of change otherwise time is a variable and with this property it holds a very unique place in space time. It is because of time that we observe changes, growth of decline or remaing the same. Time gives us to understand the universe very well.