Some Christians believe in a literal interpretation of Genesis.
One author even goes so far as to "prove" that the Genesis day was 24 hours.
Here's his reasoning:
it is abundantly clear that God communicated with precision that all creation took place during the time period of six, normal, 24-hour type days.
The Hebrew word for day (yom) can have several different meanings. The meaning is always clear when read in context.
The first reference to day in the creation account is in the context of a 24 hour cycle of light and dark, And God called the light day, and the darkness He called night. And there was evening and there was morning, one day (NASV, see Genesis One).
When the word day is used with a number, such as day one, day two, etc., it always refers to a literal, 24 hour type day. This is true 100% of the time. This holds true all 359 times that day is used with an ordinal modifier (number) outside of Genesis chapter 1.
There is no Biblical indication that day is used differently in the beginning chapter of Genesis than it is throughout the rest of the book, or the rest of the Old Testament.
The days in Genesis 1 are always specifically used in connection with the words evening and morning. This phrase is used with day 38 times in the Old Testament, not counting Genesis chapter 1. Each time, without exception, the phrase refers to a normal 24 hour type day. It is also important to note that this phrase is never used in the Old Testament in a manner which is obviously metaphoric.
When the phrase evening and morning is coupled with a numbered modifier and the word yom, there is no stronger way of specifying a normal day. We understand that Genesis is describing six Earth rotations, not an unspecified period of billions of years.
We see therefore that a study of the Hebrew text of Genesis 1 states in clear language that creation took place during the period of six, normal 24-hour type days.
Further evidence of this conclusion is given in Exodus 20:11. This passage, written in stone by the finger of God Himself, states,
For in six days the Lord made the heavens and the earth, the sea and all that is in them, and rested on the seventh day.
God, the only witness to the creation events, testifies that all things were created within a literal six day period.