Many people like Young Earth Creationists believe that the word "day" in the Bible's creation account refers to a literal twenty-four hour period. But, this belief is without exegetical evidence and ignores the facts from Scripture.
First, they ignore the fact that while the Hebrew word YOHM can refer to a literal day, it can also be used to refer to a time period. Lexicons show that the word ‘day' can be used for "time," "time of light," "a division of time," "lifetime," even "year." Evidence from sound exegesis clearly proves that the creative days cannot be 24 hours.
As "A Religious Encyclopaedia" (vol. I, p. 613) observes: "The days of creation were creative days, stages in the process, but not days of twenty-four hours each."—Edited by P. Schaff, 1894.
1.) First, a 24-hour day reference would be impossible for the first three days. This is because, while the sun and moon were evidently created before this, the fourth day was the first that the sun and moon were "placed" so as to cause a "division between the day and the night...as signs for...days and years" (1:14). The 24 hour day is dependant on the sun's relationship with the Earth. Only on the fourth day was the sun "established" (‘ASA) (1:16) or "set" (NATAN) (1:17) so as to cause this division.
2.) Next, if we exclude the 9 references to the seven creative days, out of the remaining seven references to "day" in the first two chapters of Genesis only one of them can refer to a 24 hour period (1:14b). In 1:5,14a,16 and 18, only the period of "light" is called "Day" (cf. Jn.11:10).
3.) The seventeenth and eighteenth occurrences of the word makes it clear that "day" cannot be taken literally (2:17; 3:5). Jehovah said that "in the day you eat from it you will positively die". Adam did not die within 24 hours but lived on for hundreds of years. Obviously the word "day" means a period of time here.
4.) The description of the events during each ‘day' would logically require far more than 24 hours (1:11-12; 1:20-25; 2:5- 9). Those who adamantly insist on a literal interpretation for ‘day' inconsistently claim that the "planting" "growing," "watering" and etc. are not to be taken literally, but rather miraculously occurred instantaneously. God noted that it was not good for Adam to continue by himself. If the sixth "day" was only 24 hours long why would there be a concern for Adam becoming lonely? The context indicates that for a lengthy time Adam developed a longing as he saw that there was no complement for him (2:18-20). His exclamation indicated Adam had anticipated Eve for some time: "This is at last..." (2:23).
All these activities do not seem to be describing the last part of a literal 24 hour day!
5.) Further, Gen 2:4 uses the Hebrew word TOLEDAH which means "history" (generations) to describe the whole period of creating the heavens and earth. TOLEDAH never means a short period. This whole history or time period in its entirety is then called a "day" (YOHM). This use of the word "day" to refer to all six creative days and also the prior creation of "heaven and earth" conclusively demonstrates that the word day denotes a period of time, not just a 24 hour period.
7.) Next we have the implications of Ps. 90:4 and 2 Peter 3:8. These two Scriptures do not tell us how long a creative "day" was, but they do tell us that God's "days" cannot be measured by human standards and thus limited to 24 hours!
9.) Last, but not least, is the obvious continuance of the seventh "day." Every day but the seventh was ended with the refrain "There was an evening and morning a xx day." This omission could only lead to the conclusion that the seventh day did not end back then. Further confirming this, we have the verbal statements in 2:2 & 3, correctly rendered by the NWT as, "he proceeded to rest" and "he has been resting."
The above examination of Scripture makes it clear that we cannot force God's creative "day" into a 24 hour period. This would be like saying that God must have hands like ours because this is what most other uses of the word "hand" means! The word "day" is obviously used anthropomorphically (or poetically) in the first chapter of Genesis! The meaning of "day" is simply "a measured length of time." Only the context can tell us how the writer used this term, whether in reference to "daylight," "24hrs," a "lifetime," or some "time period."