The word for day in the Hebrew language is "yom". This word can have several meanings . It can mean the daylight portion of a day, a twenty-four hour day. Some will use this word in a phrase in the day of the Lord and several other meanings. If a word can have so many meanings then how can we understand this word.
The answer is context. We must look at the surrounding context to determine the true meaning. Let's examine the contest for this special word.
When we read through Genesis one, we understand that there is an umber used each time with the word day. Is this significant? It might be because a number is used with the word over three-fifty times in the Old Testament. Each the word day explains a literal day.
In the book of Genesis chapter one, God defines the length of a day. He have the parameters with evening and morning. We can understand this idea. It is a twenty-four hour period.
I believe God is smart. I believe God would explain the days in the book of Genesis if it was a long period of time. God is not a God of confusion.