When I wrote Trial of the Demon Hunter (85k), it took me 14 months because I was only writing about 15 hours a week. (and because I was horrible at coding)
Judgement of the Fallen (110k) will have taken about 7 months because I was writing about 40 hours a week on average.
I’ve also been steadily inching away at Colonising Kepler 62e: Inception for about 7 months, and I’ve written about 24k for it so far. With this title, I’m only writing about 8 hours a week (plus, I find it much harder to write science fiction than fantasy.)
I stay motivated because I want to be able to keep writing at this pace for the rest of my life 