Time is the essence of relativity.
Time exists because of relative changes in mass and energy.
Imagine that the time has stopped. All you can visualize is that nothing moves. Everything becomes static. If you are conceptualizing a scene in a science fiction movie, you will want to show the stopping of time as a fixed scene where nothing moves - absolutely nothing. It is not just the people who have stopped, everything has stopped, the Sun, the Earth on its axis, our galaxy in its orbital path, every mass in nature, even the rays of light should have stopped, even the electrons in their orbits should not move. Everything is absolutely still. If there is no movement, there is no time.
If time is just a reflection of relative movement of objects of mass and energy and nothing else, then does time exist as an entity?
No, the existence of time is as true as the existence of darkness. Both are nothing but a reflection of something else. in case of darkness, it is light. In case of time, it is relative movement, which itself is a measure of space.
But do we fully understand space?
I would say no. One could also think of space as a measure of time taken by mass for its movement from one point to another. If light moves from point A to point B in x time, the space between point those two points must be y. This assumes that movement is an entity, and the speed of that movement is fixed.
Then do we understand movement?
Movement is nothing but the change of space coordinates of a point of energy or mass at different points of time. So movement is nothing but a reflection of time and energy/mass.
Each of these basic dimensions is a reflection of the other, and in that sense none of them actually exist.
Time, space and energy all form a continuum which is not separable from each other. Our understanding of each of these is dependent upon our understanding and perception of the other two. Remember, it was not long back that we first realized that energy and mass are actually the same entity. Space and time may also be the same, though we are not yet able to conceptualize and prove it in a logical manner.
The big bang theory demonstrates this universe as nothing but a state of interconversion of mass and energy. Space and time may be just a reflection of this interconversion.