You are making the assumption that the description of creation began then, when it may just simply be a generalization, a statement of the thesis of the coming six days (seventh rest) of creation. It would be like if I described my day to you.
Before the sun rose in the morning, i Awoke, and headed to work. I a woke from my slumber shook my head, and rolled out of bed (minute 1). Then i slowly walked to the bathroom to do bathroom things (minutes 2-7). Then I headed downstairs, started up my computer, opened twitter, and email, and began reading the news (minutes 9-25) etc. All of these things were done in the beginning of the day, and the breakfast had yet to be consumed.
See what I'm saying, don't confuse the literary style of how genesis's creation account is presented, with some bullet point list, verse, by verse of the order of creation. Day 1 isn't verse 1, Day two isn't verse 2, It doesn't quite work out that way, even if you try to stretch it. It reminds me a bit of the intro to one of the LOTR moving, when it talks about what happened in the beginning etc.