2nd Peter 3:8, from the King James:
"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."
Note "as one day" and "as a thousand years". These are similes, and should not be taken as a definition of a unit of measure here. That passage is explaining that even though it seems like God is taking forever to come back to earth and set up his kingdom here, you should "not be ignorant of the fact" that God experiences time differently from us and you can't impose your sense of urgency on him. This has nothing to do with the creation story.
Genesis is translated from Hebrew and the word "Day" in Hebrew simply implies "a very long time."
Except that if you actually read the bible, it describes a "day" as the progression from morning through evening. --
"And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day." Gen 1:5 (KJV)
"And God called the firmament Heaven. And the evening and the morning were the second day." Gen 1:8 (KJV)
"And the evening and the morning were the third day." Gen 1:13 (KJV)
I think I've made my point.
The Bible does not include the creation of Earth itself - or the universe as apart of the six creative days.
If you read Genesis again you'll notice that it says "In the beginning God created the heavens and the earth."
Then it goes on to describe the Earth's condition and then the process of the six creative days in which God made Earth habitable for life.
If you read genesis again, you'll realize that after it says "In the beginning, God created the heavens and the earth" it begins a description of the process of creating the heavens and the earth, or else Genesis 2:1 would not make sense, which reads:
"Thus the heavens and the earth were finished, and all the host of them."
Right before it explains that God rested on the seventh day. The most logical interpretation of Genesis 1 here is that it says "In the beginning God created the heavens and the earth, this is how he did it." not "In the beginning God created the heavens and the earth, this is how he made it fit for life"