ChristianAnswers.Net WebBible Encyclopedia
Today, days begin and end at midnight. This was not true of the Jews. Their days begin and end at sunset (Lev. 23:32).
The Jewish day was originally divided into three parts (Ps. 55:17).
The division of the day by hours is first mentioned in Dan. 3:6, 15; 4:19; 5:5. This system of time-keeping was borrowed from the Chaldeans. Sunrise to sunset was divided into 12 hours, and the hours were of variable length depending on the length of sunlight (John 11:9).
The word “day” can sometimes signify an indefinite time (Gen. 2:4; Isa. 22:5; Hebrews 3:8, etc.). In Job 3:1 it indicates a birthday, and in Isa. 2:12, Acts 17:31, and 2 Tim. 1:18, the great day of final judgment.
Although the Hebrew word for day (yom) can have several different meanings. The meaning in the Bible is always clear when read in context. The first reference to “day” in the Bible is in the context of a full rotation of the Earth, a full 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” (yom) 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 used specifically 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.