I agree with Daniel. See also Ex. 34:17, which says exactly in same thing in Hebrew.
But before you jump to any conclusions about what the absence of a preposition might mean, think about the rest of the verse: God created the heaven and the earth in the context of these 6 days, and rested on the 7th day. What in the universe is there besides the heaven and the earth? He's talking about 6 days somehow or another and saying that everything in the universe was created with some sort of relation to those 6 days. Like it says in Genesis 1, if you want a more detailed account of it. I don't see how you can go anywhere with this, unless you want to go with the other conventional ways of esacping six-day creationism (not a literal day, gaps inserted somewhere, etc.) which also are a twisting of the plain meaning and not supported by the text or by exegetical principles and make no sense with regard to the 4th commandment. But maybe you can show me a different theory I wasn't aware of. :-)