If you think about it, since there is no ‘time’ in eternity, then there’s no “point in time” in which only God exists and another “point in time” in which both God and time exist.
Think of it this way: how is the basic unit of time defined? (Then, ask yourself this question: if the way we know what is the basic unit of time doesn’t itself exist, how can time exist?)
I know you argue it. But, that’s where we note that this is a “coming-into-being” change, which has fundamental differences than other types of changes. Have you read up on Aristotle yet, in order to begin understanding the distinction?