Events flow simultaneously during a natural process. Historians claim that Galileo used water clocks and pendulums to specify time. In a water clock (or hourglass) the events we associate with time are recognized as irreversible. In a system with periodic motion or similar natural process the events we associate with time are recognized as a simple harmonic oscillator. A pendulum clock is a simple harmonic oscillator. During every instant of time the clock is in a particular state and the surroundings are in a particular state. Together the clock and its surroundings are in the stream of events flowing simultaneously. We only isolate systems that are in uniform angular motion (such as the polar arc swept by stars in the Northern sky due to the rotation of earth), or in periodic resonance, or in an irreversible flow, to invent the coordinate we call time. Today we stimulate Cesium-133 atoms with microwave radiation, observe atomic resonance, and specify 1 second of time as so many resonant periods.
Imagine witnessing Galileo's experiment wherein he starts a pendulum clock moving in simple harmonic motion. In sync with the beats of the clock he rolls a smooth round ball down a smooth track in an inclined ramp, lets the ball roll across a horizontal table, and lets the ball fall off the end of the table to the ground below. Time is the concept that the pendulum clock has a uniform period for each beat while the motion of the rolling ball makes a displacement in spatial position. There is no flow of time in any snapshot of events. There is the position of the pendulum and the position of the ball in any given snapshot or instant of time.