A debate rages regarding the meaning of “day” in Genesis. Some argue the day means what we understand it to be — a period of 24 hours — while others argue the Hebrew can mean “age”, thus the creation could have taken billions of years; some people attempt to reconcile the Bible with evolution (a situation which leaves both sides wanting. It’s just not possible to reconcile evolution with the Bible. We’ve written lots on evolution, search the site to find it).
But regarding the creation in Genesis, is it possible to know if it was a 24 hour period or billions of years? The answer won’t be found in Genesis, but in Exodus, as the 10 commandments are given:
But the seventh day is the sabbath of the Lord thy God; in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates. 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. (Exodus 20:10–11 KJV)
The context speaks of the Sabbath, and then refers to the creation by God. The context in Exodus makes the meaning clear — creation occurred in six days, with day being the common meaning we understand.