Chuck Missler wrote a superb article: Why Six Days? 
In our tiny 6,000 year program on Earth, we discover hints of greater things that are longer events than the 6,000 years or so of His current program for us in creation. If our perspective begins in Gen 1: 1 and we trust a God powerful enough to speak light into being, then the rest is imminently doable by such an incredible sentience. Book shelves are filled with tomes to help with your decision. For me, I am cool with 6 days inside the singularity event horizon at the beginning of time. I am also cool with the bazillion year gap between Gen 1:1 and Gen 1:2. I do not argue about it, anymore. I prefer telling people about Jesus and challenging them to answer the question – “When does God start telling the truth? Gen 2? Gen 5? For me, it is Genesis 1: 1 when it is revealed that “God created the Heavens and the Earth.” After that statement, and having faith in it, I decided that God did what He wanted and hid His secrets like Easter Eggs for His children to discover and unwrap.
This article defines why I think God did it in six days. I extensively use Chuck’s article, below, in working through why I think God did Creation in six days. For more of the deeper scientific reasoning, go to the back and Appendix 1.
The Book of Genesis presents a disturbing problem for many Bible-believing Christians. Did God really create the heaven and the earth in just six 24-hour days? How does a serious student of the Torah – the five books of Moses – reconcile the Genesis account with the “billions of years” encountered in the dictums of astronomy, geology, et al?
Many continue to attempt to circumvent the problem by assuming that the six days represent “geological eras,” or that the traditional text is simply a rhetorical “framework” for a literary summary of the creative process. Various forms of “theistic evolution” have been contrived in attempts to reconcile the Biblical text with the various theories and conjectures which dominate our evolution-based society.
However, the sincere student cannot escape the confrontations which result from the straightforward reading of the text with the ostensible declarations of “science.” How can we deal with these fundamental issues?
The thing for you and me to understand is that our eternal destiny will be determined by the “world view” each of us uses in addressing these issues. There are really only two world-views: either everything – including you – is the result of some kind of cosmic accident, like paint splattered randomly on a surrealist artist’s canvas, or this is all the result of a deliberate design by a Designer.
The darkly amusing context in my mind is that today’s ‘Spiritism’ has nothing that is “New Age” in its philosophies and worship. To date, in all the history I’ve studied, very little is new. Much of it comes from Babylon, just after the Great Flood. Before I go any further on this rabbit trail, let’s get back to ‘Six Days.’
It seems that the big question among people who are increasingly sceptical is: Who Really Wrote the Torah? One of the reasons for this scepticism is to question Six Days.
There are those who have suggested the books authored by Moses (Genesis, Exodus, Leviticus, Numbers, Deuteronomy), were actually compilations by a number of redactors over the years – the common “Documentary Hypothesis” being one of the most prevalent theories. Allow me to save you many hours of boring library research. I know who wrote the Books of Moses: Moses did. How do I know? Jesus Christ Himself said so! Many times. 
John 5: 45 – 47 Do not think that I will accuse you to the Father: there is one that accuseth you, even Moses, in whom ye trust. For had ye believed Moses, ye would have believed me: for he wrote of me. But if ye believe not his writings, how shall ye believe my words?
The account of the creation of the universe in six days still is a “bone in the throat” to many Christians. Many point out that the word for “day” is yom, and is translated to 54 other words; however, in 1181 of 1480 occurrences it is “day,” and when used with a number it is always a literal day. But the real problem isn’t the account in Genesis. It is in Exodus. In the middle of the Ten Commandments that the Creator wrote with His own finger in stone:
Exodus 20:11 For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the Sabbath day, and hallowed it.
It is undeniable that God intended us to understand that it was, indeed, six literal days. So how do we deal with the common understanding that “billions of years” was involved? How do we deal with the astronomical distances of millions of “light years” between the galaxies of the universe? Can anyone familiar with the discoveries of modern science take the Genesis account seriously?
It may come as a pleasant surprise to discover that the more you know about modern science – the real physics, not the mythology and conjectures that masquerade as “science” – the more you can take the Biblical text seriously. The Lord always rewards the diligent. A recent book includes articles by fifty top scientists – from many different fields of specialization – who declare why they believe in a literal six-day creation. 
 Matthew 8:4; 19:7,8; 23:2; Mark 1:44; 10:3,4; 7:10; Luke 5:14; 16:19, 31; 20:37; 24:27,44; John 3:14; 5:39,45,46; 6:32; 7:19, 22,23.
 Ashton, John F., In Six Days, Master Books, Green Forest AR, 2001.