it appears that day and night as we recognize it wasn't really defined until the 4th day of creation. Whether the days are consecutive 24/7 where each day of creation could have lasted say 700 milllion years, or discrete intervals of time, I don't think is too important.
another thing about 7 in the bible is that it can mean infinity.
Yup plenty of possibilities beyond the literal when it came to the ancients.