Do not we measure eventual changes in the scale of time? Don't we consider the age of the Universe till now evolved through events on the scale of time so that the absolute age of the universe is determined. These are more of my statements than questions.
Time is defined as the indefinite continued progress of existence and events in the past, present, and future regarded as a whole, and is irreversible progression.
The concept of time may not only begin due to the cosmological bodies but the requirement of time was also there in everyone’s a day-to-day life. A possibility in the requirement of time might have started locally. The ongoing Universal events those certainly indulge one in conceptualising time and accordingly time might have been conceptualized. Actually time is a concept of a uniformed scale to track events in the existence where past, present and future regarded as a whole. Time is significant because of the events, otherwise time is meaningless.
Spatial progression or spatial events necessarily needs to be tracked from above the spatial dimensions of height, depth and width, so as to avoid a likely dimensional conflict among the dimensions of space and dimension of time, hence time is conceptualised in the fourth dimension, so as to enable time to track the three dimensional existence and events through its uniformed scale. Time is therefore a human made concept, prevailing in the imperceptible fourth dimension and ticking at a constant rate for the entire universe and everything in it since its beginning.
Constancy of time is Inevitable because two variables (one is in consideration and another as reference/scale) cannot determine a variable without a constant reference/scale. Here events are variables and time as scale.
(e.g. a crystal oscillator in a digital clock and the digits displayed on the clock are two independent sections in the electronic circuit of the clock, while the crystal provides a constant oscillation as reference to the circuit and the other section of the circuit tells the time in reference of said oscillation crystal, so that a perfect synchronized time is achieved for that moment as a combined effect of the clock circuit.)
Not only present but past and future too need to be in such considerations of variable events, so time (as reference) necessarily needs to be a constant in character, not variable, but slices of time may have variable values due to their relative locations while it's mother time (as reference/scale) do not vary so that there is time difference between any two celestial objects in space.
The values of future events are not in the present consideration in the measurements of the current values but they are going be in the future values of universal events and, there cannot be any exception, as such time is continued progress through past, present and future.
Time is defined as the indefinite continued progress of existence and events in the past, present, and future regarded as a whole, irreversible progression, a concept - distinct, independent and uniformed in scale, had a beginning, resides above spatial dimension, disassociated from any of the fundamental interactions, but events (not time) are results of interactions of the fundamental interactions etc.
E.g. since time is a function of events { f(t):x→y } in the past, present, and future regarded as a whole, therefore time keeps records of the past events, tracks present events, and time will track events in the indefinite future too... a particular event what we are experiencing now that we could have experienced ten years ago too - is possible only in concept and not physically, as there would be a locational difference between the origination of light and observation of the same light, besides that the light energy would be diminished too between its origin and its observation. And for this reason time indefinitely continue its progress through the past, present, and future as a whole.