Why not? Astronomers make special rules for all hypothetical constructs including inflation, dark energy, dark matter, M-Theory, Multiverse theory, QM concepts about gravity, etc. Even creating numerous "properties" related to hypothetical entities is simply par for the course in astronomy.
Technically anything that has energy has time associated with it. Even if we *assume* a "bang", there can be no assumption about there ever being a zero energy state. Your statement of faith should read......"If all matter/energy came magically popping out of "nothing", then maybe there was a period of time when spacetime did not exist."
The concept you're trying to describe is "creation ex-nihilo" and it comes straight out of "religion", not physics.
You are of course free to disagree with Einstein if that makes you happy.