I'll try and advance the discussion as best I can.
If we look at Genesis 1:1 we are told that "In the beginning God created the heavens and the earth. 2 Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters." So there is no time frame for this process, it's a bit like "how long is a piece of string".
So even if we can nail how long each day is, we can not calculate the length of the entire process.
Defining the days or steps 1) Formation of night and day 2) Division of the waters 3) Introduction of vegetation 4) Positioning of the solar system 5) Population of the seas and air 6) Population of the mainland 7) God's rest.
Now let's have a stab at the length of a day. Raj has already offered a position, that the duration of steps 1-6 = 6000 years, and I would think (because we haven't discussed this as far as I'm aware) that his thoughts on this are based on 2 Peter 3:8
"But, beloved, be not ignorant of this one thing, that one day is with the Lord as a thousand years, and a thousand years as one day. "
So far so good. Now this is where my ramblings go slightly out of focus, because I'm heading into barely familiar territory that somebody else might be able to help with it.
There are groups out there (just google "Calculation of creative day = 7,000 years) that maintain that a creative day is 7,000 years, and although I have tried to follow the logic it's a bridge too far for me, I can't get my head around it. Having said that it has been calculated that from the time of the creation Adam to 1975 was 6,001 years detailed at this web address
http://sickleoftruth.com/1st6000years/6000P1.html
That suggests to me that maybe there is something in this idea of a 7,000 year creative day.
Sorry that I can't do better than that