Genesis 1:5 says, “And there was evening and there was morning the first day.” The Hebrew word “yom” means a 24-hour period and can also be defined as a wide range of time. So how can we correctly interpret the meaning of the text?
As we look for clues to determine the meaning of the phrase, we observe descriptive words, such as “evening” and “morning,” proceeded by an ordinal number. Hebrew scholars agree: the Scriptures clearly declare a literal 24-hour day.
Some Christians subjected to old earth beliefs, assert that the meaning of “yom” in Genesis does not determine a 24-hour period. However, God’s word can be used to expose these alternative claims. Scripture can be used to interpret Scripture: Exodus 20:8 reads, “Remember the Sabbath day by keeping it holy. For in six days the LORD made the heavens and the Earth, But he rested on the seventh day.”
It is clear that during creation week God created in six regular 24-hour days and rested on the seventh day.
(Source: Ruth Beechick – Finding Our Roots 1997 pp.13)