Thanks for the discussion on time, MD. To make your thought experiment a little more concrete, suppose that everything in the universe just “stopped” for a million years, and then started up again. How would we know? In fact, how do we know that doesn’t happen periodically? The important question, which you asked, is: Does it even make sense to talk about “time” with no change or motion? Only in an abstract philosophical construct, which may or may not be useful in describing the world around us.
In fact, that happens every time I get a letter with IRS on the return address line. I don't know about nobody knowing, but the IRS sure doesn't give a hoot.