Time is a perception, like the sensation of color. "It" does not exist independently of our mental experiences. There is no absolute flow of time, only the flow of our minds.
Even science reveals that time is not a constant feature of reality- it is a relative phenomenon. However, our ancestors long ago adapted the abstract idea of Time into a useful tool to regulate our lives. It also informs our natural sense of a temporal continuum we call History.
I thought this was an awesome visualization of the "Spiral of Time". It's enough to warp your mind into a vortex.