
The fact is that the Hebrew word yowm translated “day” can mean various lengths of time, not just a 24-hour period. For example, when summarizing God’s creative work, Moses refers to all six creative days as one day. (Genesis 2:4)
In addition, on the first creative day, “God began calling the light Day, but the darkness he called Night.” (Genesis 1:5) Here, only a portion of a 24-hour period is defined by the term “day.” Certainly, there is no basis in Scripture for arbitrarily stating that each creative day was 24 hours long.
Moses wrote his account in Hebrew, and he wrote it from the perspective of a person standing on the surface of the earth. These two facts, combined with the knowledge that the universe existed before the beginning of the creative periods, or “days,” help to defuse much of the controversy surrounding the creation account. How so?
A careful consideration of the Genesis account reveals that events starting during one “day” continued into one or more of the following days. For example, before the first creative “day” started, light from the already existing sun was somehow prevented from reaching the earth’s surface, possibly by thick clouds. (Job 38:9) During the first “day,” this barrier began to clear, allowing diffused light to penetrate the atmosphere.
On the second “day,” the atmosphere evidently continued to clear, creating a space between the thick clouds above and the ocean below. On the fourth “day,” the atmosphere had gradually cleared to such an extent that the sun and the moon were made to appear “in the expanse of the heavens.” (Genesis 1:14-16) In other words, from the perspective of a person on earth, the sun and moon began to be discernible. These events happened gradually.
The Genesis account also relates that as the atmosphere continued to clear, flying creatures—including insects and membrane-winged creatures—started to appear on the fifth “day.” However, the Bible indicates that during the sixth “day,” God was still in the process of “forming from the ground every wild beast of the field and every flying creature of the heavens.”—Genesis 2:19.
Clearly, the Bible’s language makes room for the possibility of some major events during each “day,” or creative period, to have occurred gradually rather than instantly, perhaps some of them even lasting into the following creative “days.”
When light from the Andromeda nebula takes about 2,000,000 years for that light to reach the earth, this is indicative of the fact that the universe must be at least millions of years old. Also the end products of radioactive decay in rocks in the earth testify that some rock formations have been undisturbed for billions of years.
Genesis 1:3-31 is not discussing the original creation of matter or of the heavenly bodies. It describes the preparation of the already existing earth for human habitation. This included creation of the basic kinds of vegetation, marine life, flying creatures, land animals, and the first human pair. All of this is said to have been done within a period of six “days.” However, the word yowm has meanings, which include ‘a long time; the time covering an extraordinary event.’ (Old Testament Word Studies, Grand Rapids, Mich.; 1978, W. Wilson, p. 109) The term used allows for the thought that each “day” could have been thousands of years in length.
The "Lexical Aids for the Old Testament" edited by Spiros Zodhiates for yowm expands on Strong's comments and repeatedly emphasizes that yowm can be a period of time.
As early as Genesis 2:4 we see yowm in the singular with an attached infinitive used to indicate an extended period of time. Strong's does not show this since the King James Versions retain the translation of day, but other translations recognize that in this case yowm refers to the time of the entire creation of the heavens and earth as recognized by the The Bible: An American Translation and others, "At the time when God made the earth and the heavens."
Studies are out there which show that the period called days does not mean a literal 24 hour period, but epoch’s of time. Couple that with geological studies, we can be sure that a creative day is thousands of years in length and the creation of the universe covers a time period of millions or more years.