Two conditions are required to give rise to the illusion: motion (or change, or difference) and memory.
If an object were not to change, if it remained absolutely the same, if it didn't move, grow, age, or crumble in any way (and that would also apply if you as the observer remained constant) one would not be able to feel the passage of time. (And is that not the truth: atoms never age. They show no wear and tear across of billions of years.)
Second, for the illusion to work, you would need a sense of memory to sense the passage of time. Memory enables you to compare the current situation with a previous one. Therefore, if all that you perceived consisted of the present, then time as a concept could not arise.
When you flip through a series of stills, such as what occurs when you screen a strip of film, then time will seem to pass. But it does so only because each still is a little different from the one before, plus the fact that you retain the image in your short-term visual memory. Therefore, I propose that time is a human artifact. It is the resultant illusion from flipping rapidly through a set of slivers.
Roll 'em!
