Time is a measurement of the change in the relationship between things in motions.
Time is a convention of measurement. All methods of measuring time are based on units decided in the thoughts of man. What this mean is:
Time has no existence in itself...
... just as other "dimensions" of measurement have no existence in themselves. The term dimension is an arbitrarily chosen term for expressing "a method, or methods, of measurement."
This means that none of the dimensions have an existence in the physical realm. This includes the familuar four dimensions of height, width, length, and time.
This also means that space has no existence in itself, ie: space does not "exist".
What does exist is things in motion. Time is an abstract regular measurement of the change in the relationship between the things that are in motion.
In turn, and as mentioned, space has no existence. This is why the cosmos has the potential to be ever expanding. There is no limit to the expanding of the distance between things "moving through nothingness". (I placed parenthesis around "moving through nothingness", because you really can't move through what has no existence.)
The cosmos is made up of things that are all in motion, and most are traveling at high speeds away from each other, but it is a misconception to say that they are traveling through space.
They are creating ever larger measurements of the distance between each other, but they are not traveling through space.
This is because space has no existence, ie: it does not exist, and therefore cannot be traveled through.
These ideas of time and space do not exist in the physical realm, because if they 'existed' in the physical realm they would have to have some inherent property within themselves, and they do not.
For example, the formula: E=Mc2 is much more than an explanation of energy, it is an explanation of all that exists in the physical realm, and how what exists inter-relates. It is a comprehensive description of physical existence and how it basically functions.
Note that both time and space are missing from this formula of Einstein's. They are missing because they do not exist!
This is a perfect example of Occam's razor.
What is in the formula is energy, which is equal to the same thing as matter in motion. This is what exists.
Time is a conceptual derivitive of matter in motion. It is a concept by which we measure matter in motion.
The space dimensions are actually metods of measuring things (energy and matter) which do have shape to them, and of measuring the distance between those things.
But space in itself is 'nothingness', and nothingness, in itself, has no attributes to measure.
Understanding this will change your whole view of the cosmos and what is in it.
This is a major paradigm shift, to realize that the 'dimensions are our mental constructs imposed upon existence, but not really a part of existence.
So many of NASA's "scientists" don't even realize this, and as a result, live in a science-fiction dream world, spending billions upon billions upon billions of dollars of limited resources on misconceptions about existence.