Bite your tongue! Not POE!
Seriously, at various times, he apparently told different stories about the composition of this poem. To some, he told that he just whipped it out over a couple of hours. Later, though, he wrote an essay about a lengthy construction of the work.
This applies even to the poets couple heads and shoulders above Poe, across epochs and languages. It is a general observation on their technique - although one could write an interesting research piece focusing specifically on comparison of their "filler" quality - versus the parallel comparison of respective "gem" quality.