I don't think the first days were 24 hours. The earth is slowing down. It was probably closer to 23 hrs. Genesis 1:1 is a summary sentance. Genesis 1:2 begins the actual story of Creation. In it, the author makes no question that the days were an evening and a moring (a single rotation of the earth); that light and darkness existed before the sun moon and stars and grasses and trees bearing fruit pre-dated the sun. Given that the timeline is begun from the first day to Adam, and from Adam forward through the birth of Christ, it is clear that the author wanted us to know how old the earth is. Why? What possible relevence did it have at the time to people who couldn't have understood any of it? Answer? None.
The fact that the days are ordinal (1,2,3..) and includes the 'evening' and 'morning' as a description clearly indicates a normative day. I have looked into this in the original and guess what, normally, 'Yom' or 'Day' generally means a 24 hour period aka, a day. The narrative is from the face of the earth so the sun, moon and stars were already created before creation week. 'Let there be light' simply let the light in.
He wanted to relate what he heard from the Creator concerning the creation of life on this planet and how it effected them. They had seen the miracles of the Exodus and still did not believe, at least not most of them and they died in that dessert.
Through faith also Sara herself received strength to conceive seed, and was delivered of a child when she was past age , because she judged him faithful who had promised. (Heb 11:1)
When Sara heard the promise she laughed, when the child of promise he was named 'Isaac' which means 'she laughed'. Abraham believed it the first time he heard it but when he was pushing a hundred he wasn't so sure but he believed the one who made the promise was faithful.
Faith is not about believing every promise literally as much as believing the one who made the promise is faithful.
I think that further proof of the omniscience of God can be drawn from the fact that He knew one day man would have enough knowledge to dispute His word and to draw their own conclusions about the universe around them. His one requirement for salvation is faith. Does that mean those who don't believe in His account of the creation; who doubt His word despite references to Adam and Noah by His son Jesus; those who believe that man was not created special will not find redemption? Not in itself, maybe. However, I don't want to stand in front of God on Judgement Day and have to answer why I didn't believe His word was true.
All that will matter on judgment day are the thoughts and inclinations of your heart. I have a few rules about Christian living, they include: 'turn the other cheek, go the extra mile and forgive as you are forgiven'. There is one other rule of faith with regards to the salvation of others:
But the righteousness which is of faith speaketh on this wise, Say not in thine heart, Who shall ascend into heaven? (that is, to bring Christ down from above
Or, Who shall descend into the deep? (that is, to bring up Christ again from the dead.) But what saith it? The word is nigh thee, even in thy mouth, and in thy heart: that is, the word of faith, which we preach; That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. (Romans 10:7-9)
In brief, don't ask who is going to heaven or hell, not even in your heart. Believe the one who made the promise is faithful and you will be saved.
Grace and peace,
Mark