Hello PennEd,
My feeling is that the word of God is pretty detailed regarding what was created on what day and creation of the earth was not one of them. As I said earlier, it was already there and the first thing of six days of creation is light. Now, if it said, "On the second day, God created the earth which was empty and void. And the evening and the morning were the second day," then the creation of the earth itself would be a part of that six days, but it wasn't. It was already here before anything else. And example of this is that it says that on the 4th day, the sun, moon and stars were created. And how long has been here, we just don't know.
That's my take on it anyway. I suppose we will be able to find out when see Him.