hi,
yes it does seem a bit of a stretch, but when you think about it if there wasnt a time gap, it wouldn't make sense, literally. God created everything verse 1, it wouldn't instantaneously become desolate, without form and void. And it says in Isaiah 45 also that whatever God creates is good and perfect, so the verse 1 creation we must assume would not have been desolate.
The first day reference could simply mean the literal first day of the "new world" that God was reestablishing.
And the mystery of the gap leads therefore to a completely new topic, and just how did the first creation become desolate, covered with sea and having no atmosphere?
The Bible also tells us that before this recreation, there were angels that had already been created, and also Satan who "fell from grace". The theory has been explained to me that the earth was orignally entrusted to angels lead by Lucifer, who then turned against God creating a war where the Earth was destroyed, became without form or void. Satan is then cast down to Earth and is there during the recreation, and manifests himself as the serpent that appears to Eve.
This is all pretty farfetched stuff, but is all backed up by scripture. Not something i could imagine a middle eastern man 4000 years ago could make up...