Theists will of course maintain that God can exist 'outside of time' somehow, irrespective of what physicists think. Neither will most theists be prepared to reject causality as a metaphysical principle and agree that it's dependent on time and space. They will still ask why the singularity expanded into our universe. If time didn't exist within it, it follows that there was no activity inside. It was perfectly still, yet it expanded. Understandably, it's counter-intuitive. To our mind, formed in seemingly deterministic universe, the notion of uncased event is almost unthinkable.
By broadening and/or rejecting the metaphysical principle of causality the theist is claiming that the finite past has an initial state at singularity. Singularity is atemporal since it exist at t=0 which is not a valid time. But God caused this atemporal initial state.
Thus the theist is defining God's action as a relation of production. God has an exclusive relation to the universe.
This is the only way I could make sense of an atemporal God. But it limits us to a deistic type of God. A relation of production implies that God is primarily concerned with creating universes.