Just before the 6 creation days in Genesis 1, the earth is described as ‘tohu va vohu’ (formless and void; or wild and waste; or chaotic and empty). It has no shape (un-formed) and has no stuff (un-filled).
The 6 days of creation (the ‘hexameron’) divide into 2 sets. The first set of 3 days is a ‘forming’ set, and the second set of 3 days is a ‘filling’ set. What was un-formed is formed, and what was un-filled is filled.
If God had needed to, I’ve no problem believing that a God with a different kind of power than anything we’ve seen in our universe could have created in six 24-hour literal days – or in a single moment. Heck, if God really had wanted to trick us, he could have even created all things 5 minutes ago, and given us all memories. I’m personally persuaded that the universe is very, very old, and that human beings arrive very, very late on the scene (heck, even in a literal 6-day understanding, they come last). I see this as both poetic and patient of God.
But what the author(s) of this ancient creation poem are saying with the wording and structure of Genesis 1 has to do not with ‘how long it literally took God to create’, but with a God who forms what was formless (order out of chaos), and who fills what was unfilled. ((Oh yeah, and a) that all the created things (worshipped by surrounding cultures) are not gods, b) that all the created things are ‘good’, and c) that humans have a unique role in the creation; but that’s another post.))