An interesting thing happens when you take the approximate number for the Creation of the Earth is 4.7 Billion Years ago and “homo sapiens” at between 130 - 195 Million Years Ago divided by the 5 days given in the Biblical account in Genesis 1, you get approximately 1 Billion Years and the fist life supposedly appeared 1 Billion Years after Earth Creation. So is 1 Billion Years God’s Day? To get a closer number one would need to know how those dates were arrived at and what margin of error they contain.
Dates except “homo sapiens” dates taken from Arizona University:
http://nitro.biosci.arizona.edu/...gins_of_Life/origins.html
The word for "Day" in genesis chapter 1 in hebrew is yom. Yom means one single day. This was also combined with the terms for "Evening and morning". If when Moses wrote genesis, he wanted to mean an age, he could have used a variety of different words.
He could have used Yamim, Qedem, or Olam, all of which would have implied an age, but instead he used the world Yom. (The o has a little thingy on top of it.)