A timeless being cannot create

[Belacqua]

It's difficult to have a conversation with you, because you approach metaphysics as if it were pro wrestling. Everything is a fight with you.

The OP is asking how Christian theology explains God's creation. To understand that, we need to understand Thomas Aquinas. We are looking into how a large group of other people think.

I have not said that Christian theology is correct.

Actually he didn't ask that at all. It's how you mistranslated it, into your world-view.

OP :
I think there's a logical argument to be made against God's existence here on the basis of incompatible properties. God is outside time, we're told. He's not only eternal (existing forever) but also unaffected by temporal changes.

He gets the problem perfectly. Being "unaffected by temporal changes" is not the problem. 
Using temporal concepts and ascribing then TO THE GOD, IS the problem. Creating and making time are temporal concepts and cannot be ascribed to a timeless being. 
It's as simple as that. They are incompatible and incoherent, just like a round square is incoherent. 
Aquinas didn't even get the problem.

I'm sorry that we can't have a conversation about these topics. I'm sure that if we were less combative I could learn something from you.

Please accept that you have defeated me in mortal combat and that after my terrible loss I won't be responding to you any more.