Time itself was not created by humans, we just created the ways to 'measure' it, which is, in a sense, impossible. For all we know, we're stuck inside of time and time is constantly shifting faster and slower, but we never notice it because of our location within it. This truly is a mind blowing thing to think about, because what we're measuring isn't so much time as it is time as it is relative to us and our location within it.

Since time is a constant thing and not a simple perception of the human mind, there would also have to be something that causes it, some particular THING that causes something to either be or not be affected by time, though I can't think of what would not be affected, or affected differently. Most likely something in a location on the edge of time, since time itself must, by definition, be expanding with the universe. How do you suppose time functions at the farthest reaches of the universe, where it really barely exists, hasn't got a firm grip like it does here? And how does it work on the space outside of our universe, the different dimensions into which we must, by definiton of expansion, be expanding into?

All of these questions boggle the mind.