1. What is one full day and who defined it?
It was God who defined a Day.
(Genesis 1:5) God called the light Day, and the darkness He called Night. So the evening and the morning were the first day.
2. Which day was Sun created?
The Sun was created on the fourth day.
(Genesis 1:17-19) God set them in the firmament of the heavens to give light on the earth, and to rule over the day and over the night, and to divide the light from the darkness. And God saw that [it was] good. So the evening and the morning were the fourth day.
3. Did God divide light from darkness before the creation of the Sun?
Yes. God divided the light “twice”. First in Genesis 1:4 before the creation of Sun and in Genesis 1:17-19 after the creation of the Sun.
(Genesis 1:4) And God saw the light, that [it was] good; and God divided the light from the darkness.
4. Does a creation day related to the Sun?
Absolutely not! A creation day has nothing to do with Sun because, the first 4 creation day exists even without the Sun.
5. If a creation day is not related to the Sun, how can it be 24 hours?
A creation day is not 24 hours. Bible simply puts it as a day. A day defined by God split by light and darkness.
6. What is the relation of a day to 24 hours and when did it began?
God created the Sun, Moon and the stars for signs and seasons for all his creations, not for Himself to be bound by it.
(Genesis 1:14) Then God said, “Let there be lights in the firmament of the heavens to divide the day from the night; and let them be for signs and seasons, and for days and years;
7. How can we be sure that there are two timelines – i.e., a creation day and a normal day?
(Genesis 1:4) And God saw the light, that [it was] good; and God divided the light from the darkness. (Genesis 1:17-19) God set them in the firmament of the heavens to give light on the earth, and to rule over the day and over the night, and to divide the light from the darkness. And God saw that [it was] good. So the evening and the morning were the fourth day.
8. Are there any references in the Bible that Creation day is not 24 hours, apart from the ‘lack of Sun’ evidence from Day 1 to 4?
If God rested on 7th day and we are yet to enter His rest which is on the 7th day, what day we are on? 6th day.
(Hebrews 4:4-5, 9-10) For He has spoken in a certain place of the seventh [day] in this way: “And God rested on the seventh day from all His works“ and again in this [place:] “They shall not enter My rest.“ There remains therefore a rest for the people of God. For he who has entered His rest has himself also ceased from his works as God [did] from His.
9. If there are two timelines, and if we are still on the 6th day, does this mean the earth is older than 6000 years? So, what is the significance of 6000 years?
Yes. The earth is not 6000 years old. But rather, simply older than 6000 years old. Bible never states how long was each of creation day. While the 6th day started long back before 6000 years, we never know when. However, Adam was created 6000 years back which can be calculated based on Biblical genealogies.
10. If the age of the earth is more than 6000 years, could it be billions of years?
Certainly Yes! But bible never states it how long based on normal 24 hour day. It only says, God created everything in 6 days and rested on the 7th day. While we are still on the 6th day, we never know how long each creation day is.