Well to begin (no pun intended), the cycle moves from evening to morning (thus dark to light not light to dark). But in the Hebrew this can also indicate an unformed chaos moving into orderliness. Secondly we have actually discovered the reflection of a primordial light that existed before stars and moons...and it is visible at 3 degrees Kelvin everywhere in the entire universe. The math indicates it was present at the alleged Big Bang moment (which would have included sound and this flash of radiation or light) So this explains the Light. And God said (heres the source of the sound waves), Let there be Light and there was light, and this was day one (not the same wording as the first day which is not in the text). All other repetitions of this cycle are referred to as the second day, the third day, etc. none of these can be 24 hours because that is a measure based on the revolution of the earth in relation to the Sun and neither exists at this time.
Therefore any of these days, but certainly day one, could be any non-definitive length of time (as in chromos/time). Before this day chronos/time did not even exist (which moves from one point in the past through a present moment into a future)
and directly after creation moment there still was no sun of moon so measuring a day is a matter of what that represented to God at that time not man. It is not until after suns, moons, earths, and life, and then mankind, that these represent cycles (at least to created man) that we would measure 24 hour days (notice I said we would measure it so).
Now as for the word yom translated day in Genesis 1 (the Creation story as opposed to Genesis 2 which is the story of formation), it is written elsewhere that a day unto the Lord is as 1,000 years unto man. It has been rightly pointed out that 1,000 is often used symbolically in the Bible as an uncountable number. To man at that time this is what the term represented. Ancient Hebrew did not fathom in terms beyond this. This is why the Scriptures do not mention millions or billions but only speaks in 1,000s, 100s of 1,000s, or perhaps, 10,000 x 10,000, etc.! This fact (a Hebraism) led early Rabbis and the earliest Church fathers to reckon the first six days as 6,000 years not six 24 hour days But in all fairness it could have been much longer (even millions or billions of years) or only 6 24 hour days (see the Age of the Universe by physicist, Gerald Schroeder) fo God can do what He wills (though does not always).
The Theological Wordbook of the Old Testament (1980, Moody Press) on the word "day" or yom...
"It can denote: 1. the period of light (as contrasted with the period of darkness), 2. the period of twenty-four hours, 3. a general vague "time," 4. a point of time, 5. a year (in the plural; I Sam 27:7; Ex 13:10, etc.)."
Strong's Exhaustive Concordance says...
"from an unused root meaning to be hot; a day (as the warm hours), whether literal (from sunrise to sunset, or from one sunset to the next), or figuratively (a space of time defined by an associated term), [often used adv.]:--age, + always, + chronicles, continually (-ance), daily, ([birth-], each, to) day, (now a, two) days (agone), + elder, end, evening, (for)ever(lasting), ever(more), full, life, as long as (...live), even now, old, outlived, perpetually, presently, remaining, required, season, since, space, then, (process of) time, as at other times, in trouble, weather (as) when, (a, the, within a) while (that), whole age, (full) year (-ly), younger
So day can be a day, or a year, or an age, and even an indefinite length of time. Moses, who wrote the Torah (from the LORD as well as extant sources) uses this word in all these ways. To determine what exactly is meant is discerned from the context remembering God is not absurd nor the God of confusion and from what we can know as fact.
So in Genesis 4:3 Moses writes
"And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the Lord." So we see here (directly following Genesis1) yom (day in Genesis 1) is translated time and refers to an entire growing season. 5 times in Genesis Moses uses it to mean an age or a persons age (Genesis 18:11, 21:2, 21:7, 24:1). In one instance of this application it represents the entire age of Jacob (Genesis 47:28) how ever long he lived. In Deuteronomy 5:29, 6:24and 14:23 it represents always
(wow! How long is always
?).
Later in 1 Kings 1:1, 2 Chronicles 21:19 Amos 4:4 and elsewhere the word 'yom' clearly represents a year or even years. In 1 Kings 11:42 it is 40 years. In Genesis 43:9, and Psalm 23:6 it is for ever. And lease note: it is not forever as some make it
they are separate here. Forever can only last as long as there is an ever, in the Hebrew and the Septuagint this phrase for ever (ever, being yom) implies infinity or eternal.
So there are few examples to consider. I hope this has helped.
In Christ
Brother Paul