I am not challenging a "literal" interpretation of the story in Genesis. But, to me, to interpret "day," or even the components of a "day" ("evening" and "morning"), would imply that God has a domain analgous to that on Earth, which strikes me as being just a little arrogant on the part of us relatively insignificant creatures.
We know from scientific measurements that a "day" on Earth is 23 hours, 56 minutes, and some number of seconds in length.
We also know, applying the same concept of "day" as a rotation of a celestial body through a 360 degree of arc independent of any other movement, that a "day" on Mars is about 24 1/2 of our hours. Similarly, a "day" is little over 9 Earth hours on Jupiter, and nearly 88 terrestial days long on Mercury. In fact, on lonely Pluto, a day is many Earth years in length.
So the concept of "day" is already relative within our own human experience.
It does rankle my sensibilities a tad to suggest absolute knowledge of the length of a day in the life of the Almighty.
It could indeed be roughly 24 hours, it could just as easily be 24 seconds of our time, or several hundreds of millions of sidereal years.
I am comfortable with my interpretation as a Devine day being equivalent to hundreds of millions of sidereal days because it allows many of the things we insignificant humans have been allowed by His hand to learn to fit elegantly into His wonderful mosaic.
Boy, I'm not trying to be difficult here, but that's the first time I've ever heard anyone say that interpreting the words day and night in Genesis literally as being 'arrogant.' To me, it is the exact opposite. It is humility before an almighty and omnipotent God in a struggle to grasp the enormity of His creation. It is looking at Scripture as it is, without the filter of human understanding.
This is God's word to US.......the insignificant creatures. This is HIS choice of words to communicate to us, knowing that we are finite and weak and lacking understanding......knowing our human experience.
I don't presume to know why God chose the word meaning 24 hours to talk about the days of creation, but I have to ask why would He use a specific word meaning a specific thing, and not mean it to be specific? I'm not suggesting that I have absolute knowledge of what God means, nor am I saying that I have absolute knowledge that each day is not a million years.
I just wonder why God would choose to use specific language in communicating His word to us in Genesis, instead of general language used in other portions of Scripture.