Believer says: I know the earth and universe was created in six days just as in Genesis 1.
Skeptic says: In the fourth century AD, St. Augustine wrote: “Often a non-Christian knows something about the earth, the heavens, and the other parts of the world, about the motions and orbits of the stars and even their sizes and distances ... and this knowledge he holds with certainty from reason and experience. It is thus offensive and disgraceful for an unbeliever to hear a Christian talk nonsense about such things, claiming that what he is saying is based in Scripture. We should do all that we can to avoid such an embarrassing situation, lest the unbeliever see only ignorance in the Christian and laugh to scorn.” (The Literal Meaning of Genesis [De Genesi ad litteram] Book 12).
Augustine attempted to harmonize the Bible with the science and philosophy of his day, but he warned that we can't be certain what kind of creative days they were in Genesis.
He saw creation all-at-once, so the entire act of creation took one instant. He said the Genesis account was poetical or mystical expression.
In AD 389, he said Genesis 1 was allegory so that people could understand. Years later he explained that everything was made in an instant, so creation was simultaneous. And the six days was a mystical number.
He concurred with Alexandrine church fathers (leaders) who believed creation to have happened in a single instant. The six "days" were reduced to an indivisible instant.
Related post on my other blog:
10 So, will the Earth last forever