God and time
Well, I figure that this is how they will respond to your objection: God's thoughts are eternal and unchanging and therefore timeless; all of God's thoughts are not occurring in time in the way our thoughts occur, but instead they have always been.
However, even this response doesn't make sense if God is the creator of time. The very act of creating space and time, ex nihilo, is a change; even if God is
eternally creating time and space, then God should be described not as unchanging, but as eternally changing.
However, this objection would not explain why God chooses to remain timeless as opposed to entering in time. It doesn't sound like a logical contradiction to say that a timeless being can enter into time so if God is omnipotent, then the issue remains: why is God timeless instead of temporal?
A changeless thing would be like numbers in mathematical Platonism. Numbers literally do nothing and thus are timeless in the fullest sense of the word, but God is not timeless in the way numbers are in mathematical Platonism so it is a weird description to call God changeless if God is eternally creating time and space.