I used to think the 7 days were not literal days but an undetermined amout of time, and for a few decades was an avid GAP theory proponent.
about ten years ago, I started to study about the flood, and some of the books I read also touched on creation. I have since changed my view, I guess you could say, repented from being an old earth person to now being a young earth person.
people try to look to creation to try to explain science and what we see, when we see the flood is where they should be looking, much it earth science can be properly explained by the flood, things which we think would take millions of years (the Grand Canyon for example) we come to see can be accomplished in days from a major catastrophic event.
If we start studying from this perspective and ask questions, if this happened what would we see, we can see the very things which we would expect to see. And we can also see, things which have been long held views would be impossible (the river cutting the canyon out, which would have been impossible. The river would have had to float up hill.