As I have said before, my philosophy is to unify scripture and science, rather than simply going with my first interpretation of scripture and then twisting science to fit it as young-earth creationists do. As such, I subscribe to the day-age interpretation of Genesis 1:1-31.
However, there is strong biblical evidence for the seven days of Genesis being much more than 24-hour days (which would be perfectly consistent with 4.5 billion years of pre-human history).
For one, if the writer of Genesis (probably Moses) had intended to convey seven consecutive long-eras of time (as I think they did), it could not possibly have been done in a better way. There is no Hebrew word for "age" or "era". Their only option would be to use the Hebrew word "Yom" which has multiple meanings:
1. A 24-hour day (For example, "Four days until Christmas!")
2. A roughly 12-Hour period of daylight (For example, "I worked all day.")
3. A long, yet finite, era/age of time from a few days to millions of years (I don't have an example of this one in English because we have separate words for this definition.)
"Yom" is literally the only word the author could have used to describe long eras of time. So, clearly "Yom" can have these different meanings, but which is true?
Young-earth creationists try and argue that because it is followed by "There was evening and there was morning", it must be the first definition. They apparently fail to notice that if the writer intended to convey 24-hour days, they would instead say "There was evening and there was evening" or "There was morning and there was morning".
The phrase "There was evening and there was morning" likely either acts to clearly define the "day" having a set beginning and ending, or it acts to demonstrate God bringing Light/Order from Darkness/Chaos. As Light/Order is a connotation of the Hebrew word for "Morning" and Darkness/Chaos is a connotation of the Hebrew word for "Evening". There really is no way the writer could have better articulated seven long eras of time.
Now, another major problem is that Genesis chapter 2 describes the events of the sixth "day" of Genesis in more detail, and all the events described in Genesis 2 simply could not have taken place in 24-hours. Here, I will list these events in order:
1. God makes livestock, carnivorous mammals (Or "beasts of the earth"), and rodents (Or "creeping things")
2. God makes Adam
3. God lets Adam watch the Garden of Eden grow from a desert-like area. (Note, the text is clear it "grows". God doesn't just magically make it appear from nothing)
4. God instructs Adam to cultivate and keep the Garden.
5. God tells Adam to study and name every kind of animal on earth.
6. Adam realizes the animals aren't enough for him and becomes lonely.
7. God puts Adam to sleep, and makes Eve from his side.
Genesis 1 tells us the animals, Adam and Eve were all made on the sixth "day". How on earth could this day be 24-hours?
Incidentally, certain unbelievers like to claim things like the day-age theory are "retreats" caused by modern science. Putting all the biblical evidence for days longer than 24-hours aside, I will debunk this idea by stating the fact that there were early Christians, those not influenced by modern science, that believed the days were other than 24-hours. These include Josephus, Augustine, Basil, Justin Martyr, Origen, etc.
So, considering the days of Genesis are long eras of time, here is my opinion on what exactly happened during the days in relation to the scientific record:
Day 1 (4.6 Billion BC - 4.5 Billion BC): The Sun is made, giving light to the forming solar system and dividing day from night.
Day 2 (4.5 Billion BC - 3.5 Billion BC): The Earth is made with an atmosphere and a global ocean.
Day 3 (3.5 Billion BC - 1.1 Billion BC): Plate Tectonics cause land/continents to form. God makes the first plants.
Day 4 (1.1 Billion BC - 0.541 Billion BC): The earth's atmosphere changes dramatically, reducing methane in the atmosphere allows direct visibility of the sun, moon, stars, and planets.
Day 5 (541 Million BC - 66 Million BC): God makes the first representatives of most/all modern animal phyla in the "Cambrian Explosion". These include fish, arthropods, mollusks, jellyfish and many others. God makes reptiles and amphibians. God makes dinosaurs which would eventually give rise to modern birds. Near the end of this "day", an extinction event causes all the non-avian dinosaurs to go extinct, along with many other creatures. This allows birds, fish, arthropods, and eventually mammals to thrive.
Day 6 (66 Million BC - 60 Thousand BC): God makes livestock-like creatures (most herbivorous mammals), rodents, and carnivorous mammals. God makes the Garden of Eden in the middle-east (Likely underneath the waters of the Persian Gulf now, but that’s another story altogether). God makes the first "true" humans, Adam and Eve.
Day 7 (60 Thousand BC - ? AD): God "rests" from his creative work, only sustaining his creation now. That is, until he resumes his creation on the eighth day, which has not begun yet, and will begin with Armageddon.