Time is not the fourth dimension in Physical Reality because physical dimensions cannot be non-spatial. What then is time?
Time is change, but it is more complicated than that.
If time stops, what happens? Everything changing. More specifically, everything stops moving. So time is motion.
We measure time using predictable periodic motions. One revolution around the Sun marks a year for the Earth. On rotation of the Earth on its axis marks a day. One revolution of the second hand around the face of a watch marks a minute.
However, time is more complicated than just periodic motion because we use it to measure other periodic motions. We know that one revolution of the Earth around the Sun takes about the same time as 365.25 revolutions of the Earth on its axis. We know how many times a healthy man's hear beats in one revolution of the second hand around the face of a watch. Thus time seems to be a thing shared by all objects.
However, the speed of time can be different for two different objects in two different spaces. This is called time dilation. An object on the surface of the Earth measures time slower than an object in orbit around the Earth. This is observed fact. In that case the speed of time is determined by the degree of curvature of space in any given location. Thus time seems to be a thing shared by all objects in a shared space.
I would define the term "time" as: The amount of change that happens in a periodic motion where the periodic motion measured by the observer defines the unit of time.
For example, in the case of a year time is the amount of change, at a given place, that happens over the course of one revolution of the Earth around the Sun. This illustrates that the concept of time is linked to change and to the measurement of periodic motions and finally, to the characteristics of one space relative to another space.
Time moves faster in some places than others, and this is weird.
In the past, the phenomenon of dime dilation was explained using the combination of space and time called Minkowski Space. However, if time is not a dimension then Minkowski space is not a thing in real life.
What then explains time dilation?
To be continued . . .