Chronology in the Creation Account

You're question involves at least three ideas:

1. how light can exist without heavenly bodies;
2. how time can be marked without heavenly bodies;
3. and the literary genre of Genesis 1.

The first two questions are quite easy, or at least some possible answers to them are quite easy. First, time could have been marked without the heavenly bodies because God doesn't need to look at the sun, moon, stars, etc. in order to know what day it is. Since man wasn't created until the sixth day, God was the one marking time. Personally, I think God's timekeeping ought to be trustworthy.

Second, light clearly could have existed prior to the sun and stars. This is an established scientific fact. Anybody who knows where to look can pick up a scientific textbook, an encyclopedia, and maybe even a dictionary to prove this. For example, look up the phrase "emission nebula." That's a gaseous cloud that emits light as electrons combine with protons to form hydrogen. Or perhaps one could simply ask the question, "Can an omnipotent God create a photon?" If the answer is yes, then God can create light without creating a heavenly body to emit that light. Or could God create free gas that was not gathered in a nebula and which still emitted light? Of course. Even Big Bang theorists believe there was light before there were suns. If I can flick the light switch on my wall and cause light to radiate that does not come from a heavenly body, why couldn't God have created some means of radiating light that did not require the sun, moon and stars?

The third idea related to your question is more difficult: genre. Some have argued that the literary genre of Genesis 1 is at least somewhat poetic, such as an ancient hymn that became somewhat more prosaic in its transmission over time. Others have argued that it is a metaphoric, stylized account. Still others have argued that it is simply historical narrative. None of these views challenges the truth of the chapter. The only question is: How does the literature intend to convey meaning? If the passage is metaphoric, then we may still affirm the truth that God created all these things, while at the same time denying that the literature intends to teach us the precise order or timing of his creative acts. Understanding the "days" of Genesis metaphorically does not deny that in the account as written "day" refers to what we now perceive as an approximately 24-hour period ("and it was evening, and it was morning..."). Rather, it simply asserts that the literal day in the story is a metaphor for something else (like the metaphors we find in Jesus' parables). A very similar case can be made for the use of the "days" as a literary structure.

So, there are a couple ways to answer the objections you mention. If the literature is historical narrative, then science defends it. If it is not, then literary analysis avoids any reason to consult science. And even if it is historical narrative and science is actually wrong, God's ability to do anything (e.g. create a photon) still vindicates the passage.