The question periodically arises whether God is in time or not. Theories of “A” time and “B” time keep the philosophers busy trying to untangle how an infinite, which necessarily must exist, can intervene in finite time. Part of the answer is that time is change, and since God does not change, God does not experience time while changing beings do.
Aquinas anticipated some of the objections to God and time. His work Compendium Theologiae is a summary of theology written at a more readable level than some of his more complex works. In CT 98, Thomas says:
The objection we are dealing with argues from the standpoint of an agent that presupposes time and acts in time, but did not institute time. Hence the question, why God’s eternal will produces an effect now and not earlier, presupposes that time exists; for “now” and “earlier” are segments of time. With regard to the universal production of things, among which time is also to be counted, we should not ask: “Why now and not earlier?” Rather we should ask: “Why did God wish this much time to intervene?” And this depends on the divine will, which is perfectly free to assign this or any other quantity to time. The same may be noted with respect to the dimensional quantity of the world. No one asks why God located the material world in such and such a place rather than higher up or lower down or in some other position; for there is no place outside the world. The fact that God portioned out so much quantity to the world that no part of it would be beyond the place occupied in some other locality, depends on the divine will. However, although there was no time prior to the world and no place outside the world, we speak as if there were. Thus we say that before the world existed there was nothing except God, and that there is no body lying outside the world. But in thus speaking of “before” and “outside,” we have in mind nothing but time and place as they exist in our imagination.
Here Thomas raises a valid point. With all of the back-and-forth among theologians and philosophers about how an eternal being could act in time, no one seems to care as much of why God created the world here instead of over there. (Although atheists seem to raise an objection when they invent new “universes” over there, neighboring this one, and call it another universe.) I have yet to hear anyone say “because God had to be somewhere when He created this space, then He had to be in space from eternity” or just as worse, “God may have been non-spacial before the universe was created, but afterward became a being limited by space.” We do not see any issues with God being non-spacial, yet creating a spacial universe. I suspect this is because a spacial God is one that appears to be limited by space, who must be either here and not there, or over there and not here. Such a concept is easier to understand than time, and would be blasphemous.
But somehow when it comes to time, theologians trip all over themselves trying to show that God must be limited by time, exist now and not then, but do not see such an idea as hindering God. Aquinas anticipated the time problem 750 years ago and answered it. God is eternal, yet acts in time, because God is changeless and time is a measure of change. Time is not a state of being that one is in or out of. Saying that God enters time, experiences before and after in Himself, or is somehow limited by time, is to limit God in His very being.
Just as a non-spacial being cannot become spacial, and a non-created being cannot become a created being, it is true that an eternal being cannot become temporal. However, He can do temporal acts that we experience as having temporal succession, and will an act to happen now and not later, or vice versa.