"In the beginning, God created the heavens and the earth...."
Quantum Theory. Though by the Heisenberg Uncertainty Principle, as the position and and momentum of a system can never be simultaneously known, we can never really perceive of the "beginning", although the contemporary expansion of the universe "seems" to account fairly well for a "creation event" within the constraints of the Planck Time.
Given this, it doesn't stretch credulity that such expansion by E=mc2, where mass(m) is relativistically constrained, that 15 billion years might be expressed otherwise as "6 days".
"If I knew Him I'd be Him." Yet He doesn't seem stingy in time.
In the beginning God created the heavens and the earth. The earth was without form, and void, and darkness was on the face of the deep It doesn't say when that was but as science shows it had to be millions or billions of years ago. Then we read the last 1/2 of verse 2 and it tells us:
And the Spirit of God moved on the face of the waters.
There was an "age" before this one, the one in which the dinosaurs lived and God destroyed that age. The last 1/2 of verse 2 tells us when our present, 2nd age, began. That's when the "6 days" started and even then we have to remember what Peter said - "a day with the Lord is as 1,000 years". I believe that applies here.