No change without the passage of time.
No passage of time without change.
That is almost trivial. It does not help to tell us what or why time is.
Or perhaps it does.
Perhaps time is a consumable. It is the fuel that is needed for and is consumed by change. Quantum of change per unit of time taken as miles traversed per gallon of fuel. It follows that we can stop the passage of time if we can stop change – down to the motion of the elementary particles. Time does not just pass – perhaps it has to be consumed.
Perhaps the single great mystery is gravitation. Then gravitation (or gravitational energy) is manifested as the passage of time. The speed of the passage of time then varies with the gravitational field. One real second per perceived second now, but perhaps zero at the Big Bang.
No time without gravity.
And no change without time being consumed.
So, no change without gravity and time is just the medium of change.