Though I am not currently a concordist I do tend to agree with the assertion of many Christian apologists that it is theoretically possible for the ‘days’ of genesis to be long periods of time, and for the same reasons, 2 Peter 3:8 says that God is beyond human comprehension of time, so a ‘day’ for him in my opinion needn’t be the same as a human day, it could be one, but it could also be a billion years or five seconds.
As flawed as being a Concordist may be (at least that’s what I’m continuously being told) … it seems like a much better position to be a concordist than to believe something that is patently wrong – like God doing the events of Days 1, 2 and 3, in 72 hours, despite the fact there wasn’t even a Sun to mark the days in any way at all.
In Truth, God is outside of time… he could have done everything all in an instant. The fact he doesn’t means he is conducting himself in a way that the limited intellects of humans can comprehend and interpret what is going on…
… or the writer or Genesis was just trying to apply some ART to his writings.