Time is elementary.Therefore it is not within something. Any physical theory needs time in order to show that the theory is successful in predicting future. We then deduce that the theory is correct. Therefore a physical theory which claims time as a emergent entity does not exist.
OK, now I see where you are going with this.
It is important to keep in mind that the “time”*that is used by physicists, as if it were a quantity, like distance, is only a mathematical model that fits because, for us, time “flows” in what seems like a continuous motion.
(In reality, quantum theory puts that in crisis, but more about that later.)
Time is like mass: physics provides no way of saying what it “is”; it is just a parameter that must be made to fit the model.
However, with Aristotelian philosophy, I think we can do better. Aristotle basically identifies time with
change (or, as it is sometimes said “movement”—although this includes all kinds of changes, not just changes in position). As a sort of working definition, he calls time the “measure of change according to a before and after.”
I think that definition works well, especially when we consider how we measure time. If you think about it, the universe does not have a built-in digital clock that we can take readings of. Rather, we have to take existing realities that act in a (more or less) uniform manner, with which we can
compare the progress of other processes.
For instance, before there were clocks, we would measure the time of day according to the position of the sun in the sky; the months according to the rising and setting of the sun and the position of the moon; the seasons according to the position of the sun and the cyclical changes of temperature and weather. Nowadays, we really have not fundamentally changed our way of measuring time; we just have instruments that produce a much more regular undulations: mechanical clocks, digital clocks, atomic clocks, and so forth.
We don’t have to invent for ourselves a pre-existing “entity”*that is prior to all of the changes we measure; it is sufficient for our measurements to match up in a predictable way with the regular undulations of our instruments.
That is why changeless entities—which is basically only God—do not experience time in any way. However, by creating the physical universe in such a way that it basically is in a state of constant flux, God in that very act creates time.
(Quantum mechanics suggests that what appears continuous on a “macro”*level is, in the “micro”*level, in fact, a series of transitions between a very large but finite number of discrete states. That does not fundamentally challenge the basic notion: time is simply the measure of the changes that things undergo.)