But time isn't part of my hypothesis! I see no reason why time has to be part of it. If so, how long does something have to exist in order for it to be said to have existed? The very fact that this question is, in practical terms, unanswerable* is part of the reason why I am prepared to accept the possibility that time does not realy exist.

AUGH! The question "how long does something have to exist in order for it to be said to have existed? " isn't unanswerable! Just because we may not be able to measure it or name it, doesn't mean that it doesn't exist! Mercy--
if we based our theory on that, we'd have to say that anything shorter than the shortest duration we have a name and measuring capability for, doesn't exist! That is--
let's say that a second was the shortest amount of time that we have named and measured. Would we then say that any length of time shorter than a second does not exist?
Given what we know now, no! So, I am extrapolating that, down beyond what we know of measuring time today.

And besides, if time truly isn't part of your hypothesis, then there is no need to have asked that question.

I still say that if something exists, it exists in a period of time. And that goes for tsuwm's Before the Big Bang theory, too: there was something there, that all of these celestial (isn't that a lovely word?) bodies were formed from. So, I think there was time, then, and probably also changes of some kind, that marked the passage of time. Even if it was nothing more than all the little electrons and quarks and things moving in their little orbits, something happened.

I think that if anything changes, that is indication that time has passed. Hmm--I was going to say that if a true vacuum existed, then perhaps there wouldn't be time inside it. But as far as the Big Bang theory goes, all this mass couldn't have suddenly sprung into being from a vacuum! It just couldn't have. But since I can't quite get my mind around the concept of a universe that contains a vacuum, with...something...affecting it from outside, let me go here: let's say that scientists have created a perfect vacuum inside a container. Is there time inside that container? I say yes! If light falls on it, and changes with the turning of the earth, that's a change inside the container. Okay, let's say the container is opaque: what about changes in temperature, or in whatever the container is resting on? Gravity shouldn't affect the vacuum, but changes in temperature might, if they affect the container by altering its size slightly.

I don't think we can stop time. Not today, but possibly in the distant future. I don't think time will ever run backward, though it may eventually become possible for humans to travel back through it. Whew, what an exercise!
Cool discussion!