I don't know either, but we are not completly in the dark. If Satan was created, it would be between Genesis 1:1 and the meeting with Eve in the garden. Of course there were other things that would have had to happen in this time frame. Do we need a gap or gaps and if so where would they be?
Revelation 12 says "his tail drew the third part of the stars of heaven." The stars were made on the fourth day so if the stars are the fallen angels, that might suggest they were made on the fourth day.
Perhaps you already see a problem here. Genesis 2:3 seems to distinguish between "created" and "made" and nothing was created on day four.
The details in scripture give us much more than we recieve. Look closely at the details.
I'm headed out right now we can discuss more later if you like.
Seven
The record in Genesis deals with God's creation of our physical world (universe) culminating with the crown jewel - humans (created in the image of God). It does not specify that He created the angels during this time. Perhaps He had created the angels much before (and heaven as well). Was there the passage of time before God created it in Gen1:2?
The fact that Revelation states that stars were cast down I don't believe refers to our physical stars that were created on day 4 but rather that they are heavenly beings. Much like the dragon in that same passage is not a physical dragon but Satan himself "who masquerades as an angel of light". In Isaiah, there is a reference to the morning star and how he said in his heart I will ascend to heaven, I will raise my throne above the stars of God (Isa 14:12). This is in reference to Satan pridefully boasting to be more important than the other angels and so much so that he will be "like God". These star references are not our physical stars but angelic, heavenly beings. There is a lot of metaphorical, pictorial depiction in Revelation and I get confused as to when it is literal and when it is metaphorical. This is one of the passages I really don't think refers to literal stars.
If the above is true, then there is no problem in maintaining the integrity of a 6 day creation and the concept of sin/death being introduced through Adam and subsequently to us, his seed.