My understanding of science is rudimentary at best and I'm not much better at theology. But I'll give you some possibilities:
1. At what point in the First Day did God command light? As there was no differentiation between night and day, that day could have been thousands of years.
2. On the Second Day He created the firmament, this WOULD HAVE affected gravity and the Earth's rotation possibly shortening the duration of the day.
3. The Third Day the waters were gathered and dry land was created, so during these two days which could have lasted ANY LENGTH OF TIME anything could have happened in the seas.
4. Also, on the Third Day, vegetation was created; however, on the Fourth Day God said, "Let there be lights made in the firmament of heaven, to divide the day and the night, and let them be for signs, and for seasons, and for days and years."
So, what we have are four days that lasted an undetermined length of time, this could have been thousands even millions of years.
Yes.... as a science major in my undergrad studies(and in my doctoral studies) I really struggled with this. I did a lot of study on it, focusing my reading largely in the young earth creationism camp. I'll probably never be convinced of anything older than, say, 12,000 to 15,000 yrs, but it is much less of a concern for me lately.... it's just that you really have to stretch the scriptures to match the 'findings' of the secular scientists.
I know how research can go if you have preconceived ideas. I was a Howard Hughes Medical Institue Fellow and did my own molecular biology research and I've seen studies tweaked this way and that to yield any number of supports for preconceived ideas. Being from the 'sola scriptura' camp, I take the scripture as authority..... and it seems that if the Lord were communicating the details of the creation with the old testament saints in the manner that he did, he intended the readers to understand that they were normal days and not millenia or even more.... it just smells too much like compromise in the face of a growing contingent of secular science.