Hi,
A few people have suggested that the creation days are 'God days' i.e. they are of an undetermined timespan. Some would maintain that a day is like a thousand years to the Lord, so each creation day was a thousand years long.
An evening and a morning suggests that it was a 24 hour period, but, since there is no morning or evening on the 7th day perhaps these 'days' are of an undetermined time.
However, there are a few problmes with this, in most cases the word 'yom' can mean nothing other than a 24 hour day off the top of my head I'd say Numbers 7:12-83, the 12 days of dedications to the tabernacle, has to mean 24 hours, the Hebrew 'yom' is used in every instance of 'day' in these verses.
I think you are making a mistake by thinking that evolution negates creation, they are compatible as evolution does not present an explanation as to where the first lifeform came from, it is only used to explain the diversity of life.
I would say that things evolve, and that evolution of life is the most documented and authenticated fact in all of human history.
Brian.