God didnt create us over billions of years. He has the strength to do it in any time frame He saw fit. Which just happened to be 7 days. He can/could/will expand the universe that He created in any time He sees fit as well. We as imperfect humans may not have the capacity to understand His greatness.
How do you know?
a day is the time it takes for the earth to rotate. so if the earth did not exist during day 1 ... day 2 .. who was keeping time?