There are several issues mixed up, like spaghetti, in the original post.
In science, a theory is an explanation that has a lot of support. It may eventually be overturned, but at least up to a point, it is usually the best explanation for observable phenomena.
The term “hypothesis” is an assertion that a scientist tests to see if it can support or detract from a theory. A hypothesis can be hard to prove or disprove, and it may take many years to answer the question posed by the hypothesis.
The Bible is not a science book. Many people certainly took it to be such, for centuries.
Science may be said to hold the hypothesis that there was no “beginning.” Many scientists study physics and math to prove that there was no beginning, and are looking for ways to describe what there was BEFORE what we have so far called the “beginning.”
the Bible was written for believers and it makes sense only to believers. Yes, people have tried to assign a time to the creation, by working backwards, and estimating what the length of generations might have been, coming up with figures like the Jews, who say this year is something like 5784 since creation.
Modern biblical research tends to shy away from making such calculations. In the gospels, the generations don’t mean that they were actual successive generations, which is the assumption of those who make the estimates.
the Catholic Church encourages scholars to research these questions, of course, but the goal it to discover what God wants to teach us from the scriptural account.
the subject of inerrancy is actually a negative statement, that the bible teaches us no errors with respect to our faith. that is recognized as being a long ways from saying that every statement in the bible is a positive statement of historical and scientific validity.
For example, we know that the earth turns on its axis. That produces day and night. any reference to the sun rising or setting is a form of expression that is meant to carry the thought of a religious truth. It is not nor was ever intended to convey scientific exactitude.