If you spent the time reading me, you'd see that God had two different sources of light.
The one in Genesis 1:3 could not have been the big bang, because there were three full-days days before the creation of the sun. If we say that there was a big bang on the first day, based on the fact that God said, "Let there be ligt", then we have to fully accept that there was a big bang also on days two and three.
The reason for this is that we know that days one, two and three had the same source of light.
Anyone who can read knows that He created the sun and the moon, along with the other stars on the fourth day. How difficult is that to understand?
If you feel inclned to believe that the "Let there be light" light of the first day was the big bang, then you have to tell me why it cam back also on the second and third day to provide light.
Pretty simple. First there was nothing. Then there was light. That light did not go away. We know that light produces matter and matter produces light. God made matter from the light. Some of this matter turned back into light. Those are stars among other things.
God being infinite and timeless is no respecter of time, in other words time does not limit God. So when he talks of time there is no prerequisite for him to follow our convention. Thus Jesus can say --- Jhn 8:58 Jesus said unto them, Verily, verily, I say unto you, Before Abraham was, I am.