In a nutshell, I understand those to be literal days, just like the days we have today. I have no problem acknowledging the fact that God created the universe, and as the master of such, can find no reason to need to resort to God taking billions of years to do what an omnipotent God could do in an instant. The pattern of evening and morning are there as precedent for us.
'And God saw every thing that he had made, and, behold, [it was] very good.'
If every thing God had created, including man, was good, that in and of itself shatters the myth that billions of years of evolution were necessary to get us to day 6 - implicit in the theory of evolution is the realiziation that what came before was imperfect, and denies the very existance of a Creator.
As a people, we craft answers to fit the apparent problem. Through the centuries, all of our scientific endeavors have us continually adjusting and refining our answers for those same problems. How can a photon travelling at the speed of light occupy the mass of the entire universe (relativistically)? The final scientific answers have not been discovered, nor will they ever. Even today, after millenia have passed, not a single person can create matter from nothingness, nor can any scientist explain how it could be done. The devil is the author of confusion, and his purpose is to lead us away from the truth.
I prefer to believe that God, in His infinite wisdom, created this universe in just a few days, that everything was good before death entered into the equation, and that He loved us enough to send His only Son to die in our place. We, who deserved nothing, were given everything.
On the subject of photons, mass and relativity, you might be interested in this article.