The first part of Genesis indicates that the earth could have existed for billions of years before the first Genesis “day,” though it does not say for how long. But itt does describe what earth’s condition was just before the first “day” began, “Now the earth proved to be formless and waste and there was darkness upon the surface of the watery deep; and God’s active force was moving to and fro over the surface of the waters.”...Genesis 1:2.
Many people consider the word “day” used in Genesis chapter 1 to mean 24 hours. However, in Genesis 1:5 God himself is said to divide day into a smaller periods of time, calling just the light portion “day.” In Genesis 2:4 all the creative periods Or 'days' are called one “day”: 'This is a history of the heavens and the earth in the time of their being created, in the day [all six creative periods] that God made earth and heaven.”
So all the creative days were talked about as one day.
The Hebrew word yohm, translated 'day,' can mean different lengths of time. Among the meanings possible, William Wilson’s Old Testament Word Studies includes the following, 'A day; it is frequently put for time in general , or for a long time; a whole period of time . Day is also put for a particular season or time when any extraordinary event happens.” This last sentence to fit the creative “days,” for certainly they were periods when extraordinary events were described as happening. It also allows for periods of time that are much longer than 24 hours.
Genesis chapter 1 uses the expressions “evening” and “morning” relative to the creative periods. Does this indicate that they were 24 hours long? Not necessarily. In some places people often refer to a man’s lifetime as his “day.” They speak of “my father’s day” or “in Noahs' day.” people may divide up that lifetime “day,” saying “in the morning [or dawn] of his life” or “in the evening [or twilight] of his life.” So ‘evening and morning’ in Genesis chapter 1 does not limit the meaning to a literal 24 hours.
“Day” as used in the Bible can also include summer and winter, and the passing of seasons. (Zechariah 14: 8 ) “The day of harvest” involves many days. (Compare Proverbs 25:13 and Genesis 30:14.) A thousand years are likened to a day. (Psalm 90:4; 2Peter 3:8,10) “Judgment Day” covers many years. (Matthew 10:15; 11:22-24) It would seem reasonable that the “days” of Genesis could likewise have embraced long periods of time—millenniums. What, then, took place during those creative eras.
Now for the light question.
“‘Let light come to be.’ Then there came to be light. And God began calling the light Day, but the darkness he called Night. And there came to be evening and there came to be morning, a first day.”...Genesis 1:3,5.
Of course the sun and moon were in outer space long before this first “day,” but their light did not reach the surface of the earth for an earthly observer to see. Now, light evidently came to be visible on earth on this first “day,” and the rotating earth began, to have alternating days and nights.
The light came in a gradual process, extending over a long period of time, not instantaneously as when you turn on an electric light bulb. The Genesis rendering by translator J.W. Watts reflects this when it says: “And gradually light came into existence.” (A Distinctive Translation of Genesis) This light was from the sun, but the sun itself could not be seen through the overcast. Hence, the light that reached earth was “light diffused,” as indicated by comments about verse 3 in Rotherham’s Emphasised Bible.
Then the bible goes on to talk about the second 'day' or period of time.
