The problem is very simple. "time" is an abstract concept, just like the Arabic number 1 / 2 / 3, which is an abstract concept that we have created to understand the world. They do not exist in themselves, and there is no physical form of matter.
Time is a physical quantity, and therefore, it can be measured. In SI system, the second is the unit to measure time. A second is defined as the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of cesium 133 atom.
Not only time, every single thing in the universe depends upon how we feel at the moment.
A day before marriage, a day before farewell, a day before flight. Three conditions. Same time interval. Big contrast in feelings and how we perceive time. Whether we are filled with joy or anguish or caution or curiosity or sadness , time feels different. It's all about how we feel. Yes,Time is eternal and can't be controlled as all say but we can control the effect of time and that's the best thing.
Before the clock; peole used to know the time of the day by the position of the sun in the sky and count the days and months by the size of the crescent and the moon. It is all about rotations of the moon and earth.