Most of the time taken up is worldbuilding research, character development, and plot outlining. That can take years, or at least several months.
When all of that is done, I can hammer out 10,000 words in about one week...provided that I don't do anything else but eat, sleep, and use the bathroom.
And, you know, provided that the story itself can stretch over that many words given my personal sense of description. I can get into the mindset to win NaNoWriMo, for example, but I never have because my stories are done at around 30,000 words.