Actually, rather than assuming, I trust that God and his words are true. Since he wrote the DNA for all living things why should anyone assume different meanings for his very plain and straightforward words ~ there was evening and there was morning ~ the same way we measure days today.
Furthermore, how do evolutionists explain the 7 day week?
Month = approx lunar cycle and year = solar cycle but what about that pesky week?
So you don't "assume", you "trust that it's true", and you expect that to pass for an explanation of the difference? Seriously?