Einstein made a grievous error in his assumption about time in his theory of relativity. He claimed time is 'the hand on a clock'. Come on, Albert, we're doing physics here.

Time is a human invention based on the angular velocity of the Earth's rotation. In the Egyptian era of the Pharoahs, they used sun dials and no one talked about time as an entity that could expand or contract. Einstein et al should have clued in that Sun dials offer time as the position of the Sun in the sky. Ergo, it has to be related somehow to the relative position of the Earth as it rotates.

Fast forward at least a 1000 years when sailors were sailing the ocean blue. They could get their position north-south using a sextant and the angle the horizon made with the Sun at noon. The Sun, again, and the horizon, representing the relationship between the Sun and the rotating horizon. The sailors needed a time-piece, not to measure a phenomenon called time, but to generate it. They needed to keep tract of the displacement of their ships from a certain point on land.

Time came into being when someone set up a machine to synchronize with the rotation of the Earth. They measured the position of the Sun and allowed the machine to run till the Sun was in exactly the same position the next day. The day, as we know it now, had yet to be invented but when the rotating device had a mark indicating the amount it had turned between Sun sightings, that became the length of a day. It was a matter of then gearing the device to turn exactly once between daily Sun sightings and the clock as we know it today came into being. Obviously it was modified to create 2 x 12 hour periods but some people still use the 24 hour clock.

Back to the oceans. The sailors needed distance markers so someone invented a system of dividing the 360 degrees around a circle of latitude in 24 equal segments of 15 degrees each. Why 24?? Don't know. Anyway, those 24 divisions became lines of longitude and the hour. That's right, an hour of rotation is about 15 degrees of rotation. They needed smaller divisions, however, so the hour was broken into minutes and seconds and so was the 15 degrees of longitude.

Time and the Earth's angular velocity/displacement go hand in hand. Since the Earth's angular velocity is a constant for all intents and purposes, so is time. The Earth's rotational velocity does vary by fractions of a second but that does not amount to a hill of beans. Newton claimed time is absolute and Einstein argued that time can dilate. Seems E. was wrong, so there goes space-time curvature and all the modern pseudo-science about gravity not being a force but an anomaly of space-time curvature.