A conjecture is not a theory. It is weaker than a theory. That's why we have two different words. If a conjecture were a theory, we wouldn't need a different word for it.
The biblical account does not specify how long a year is. The word was spoken and had a conventional meaning long before Moses wrote it down. I doubt it was 365.25 days.
If the year were 50 days, most of the worlds plants, which are genetically programmed based on a 365 day growning season, would have become extinct.
In my way of thinking, all theory is conjecture, but not all conjecture is theory. Do we agree?