Here is another excerpt from this article at Aish:
What is a "day?"
Let's jump back to the Six Days of Genesis. First of all, we now know that when the Biblical calendar says 5700-plus years, we must add to that "plus six days."
A few years ago, I acquired a dinosaur fossil that was dated (by two radioactive decay chains) as 150 million years old. My 7-year-old daughter says, "Abba! Dinosaurs? How can there be dinosaurs 150 million years ago, when my Bible teacher says the world isn't even 6000 years old?" So I told her to look in Psalms 90:4. There, you'll find something quite amazing. King David says, "One thousand years in Your (God's) sight are like a day that passes, a watch in the night." Perhaps time is different from the perspective of King David, than it is from the perspective of the Creator. Perhaps time is different.
The Talmud (Chagiga, ch. 2), in trying to understand the subtleties of Torah, analyzes the word "choshech." When the word "choshech" appears in Genesis 1:2, the Talmud explains that it means black fire, black energy, a kind of energy that is so powerful you can't even see it. Two verses later, in Genesis 1:4, the Talmud explains that the same word -- "choshech" -- means darkness, i.e. the absence of light.
Other words as well are not to be understood by their common definitions. For example, "mayim" typically means water. But Maimonides says that in the original statements of creation, the word "mayim" may also mean the building blocks of the universe.
Another example is Genesis 1:5, which says, "There is evening and morning, Day One." That is the first time that a day is quantified: evening and morning. Nachmanides discusses the meaning of evening and morning. Does it mean sunset and sunrise? It would certainly seem to.
But Nachmanides points out a problem with that. The text says "there was evening and morning Day One... evening and morning a second day... evening and morning a third day." Then on the fourth day, the sun is mentioned. Nachmanides says that any intelligent reader can see an obvious problem. How do we have a concept of evening and morning for the first three days if the sun is only mentioned on Day Four? There is a purpose for the sun appearing only on Day Four, so that as time goes by and people understand more about the universe, you can dig deeper into the text.
Nachmanides says the text uses the words "Vayehi Erev" -- but it doesn't mean "there was evening." He explains that the Hebrew letters Ayin, Resh, Bet -- the root of "erev" -- is chaos. Mixture, disorder. That's why evening is called "erev", because when the sun goes down, vision becomes blurry. The literal meaning is "there was disorder." The Torah's word for "morning" -- "boker" -- is the absolute opposite. When the sun rises, the world becomes "bikoret", orderly, able to be discerned. That's why the sun needn't be mentioned until Day Four. Because from erev to boker is a flow from disorder to order, from chaos to cosmos. That's something any scientist will testify never happens in an unguided system. Order never arises from disorder spontaneously and remains orderly. Order always degrades to chaos unless the environment recognizes the order and locks it in to preserve it. There must be a guide to the system. That's an unequivocal statement.
The Torah wants us to be amazed by this flow, starting from a chaotic plasma and ending up with a symphony of life. Day-by-day the world progresses to higher and higher levels. Order out of disorder. It's pure thermodynamics. And it's stated in terminology of 3000 years ago.
The creation of time.
Each day of creation is numbered. Yet there is discontinuity in the way the days are numbered. The verse says: "There is evening and morning, Day One." But the second day doesn't say "evening and morning, Day Two." Rather, it says "evening and morning, a second day." And the Torah continues with this pattern: "Evening and morning, a third day... a fourth day... a fifth day... the sixth day." Only on the first day does the text use a different form: not "first day," but "Day One" ("Yom Echad"). Many English translations make the mistake of writing "a first day." That's because editors want things to be nice and consistent. But they throw out the cosmic message in the text! Because there is a qualitative difference, as Nachmanides says, between "one" and "first." One is absolute; first is comparative.
Nachmanides explains that on Day One, time was created. That's a phenomenal insight. Time was created. You can't grab time. You don't even see it. You can see space, you can see matter, you can feel energy, you can see light energy. I understand a creation there. But the creation of time? Eight hundred years ago, Nachmanides attained this insight from the Torah's use of the phrase, "Day One." And that's exactly what Einstein taught us in the Laws of Relativity: that there was a creation, not just of space and matter, but of time itself.
Einstein's Law of Relativity.
Looking back in time, a scientist will view the universe as being 15 billion years old. But what is the Bible's view of time? Maybe it sees time differently. And that makes a big difference. Albert Einstein taught us that Big Bang cosmology brings not just space and matter into existence, but that time is part of the nitty gritty. Time is a dimension. Time is affected by your view of time. How you see time depends on where you're viewing it. A minute on the moon goes faster than a minute on the Earth. A minute on the sun goes slower. Time on the sun is actually stretched out so that if you could put a clock on the sun, it would tick more slowly. It's a small difference, but it's measurable and measured.