Peter tells us that to God, a day is like a thousand years (meaning a very long time). I see no reason to be held to the notion that a day has to be measured by the rotation of a single planet in such a massive universe. 24 hours is completely arbitrary, especially when you consider that the Earth didn't always rotate at that pace.
As for the Big Bang and creation, we can argue the finer points until the end of time, but the one truth we can't deny is that God created the universe out of nothing, else we would be saying that some things were not created by God. With this is mind, what else would the moment of creation look like, besides an explosion of matter from essentially nothing?
Now I am still suspect of evolution, simply because the fossil record doesn't really support it in the Darwinian sense. Basically, in one set of rocks you have a specific set of species, then there appears to be a mass extinction, followed by another layer of rocks whose fossils present a completely different set of species. You can kind of align which species are related to each other in the different layers, but what you cannot find is a gradual transition as species evolve. It's almost as if they change overnight (geologically speaking). What does this mean to both creationists and evolutionist? I don't know, but I find it intriguing that it has never come up in debates.
I have not closed the door on evolution because Genesis tells that God formed man out of the dust in the earth and then breathed life into Adam. One way to look at this is that God may have built up man from the ground to his present form through evolution before infusing him with a human soul, by breathing life into Adam's nostrils. Not saying that is the way it happened, but I think it is a reasonable theory.
What I find to be unreasonable is to claim that a person's state as a Christian and whether or not they are truly saved can be discerned by how they understand Sacred Scripture. We are not Gnostic. We are not saved by special knowledge or understanding. We are Christians in the Pauline tradition. We are saved by our faith in Christ Jesus--nothing more or less. Regardless of how we understand scripture, as long as we place our faith and hope in our Lord Jesus and follow his commands to best of our ability, we can be confident of our salvation.