When I read it, it took approximately 2 weeks. Which is about what I expect when reading the equivalent of an entire book series. Definitely worth your time, though don't get any ideas about reading it all in one sitting.
Thread Tax: Ignoring manga, the most recent tale I finished was Promise of Blood, a swords-n-sorcery-n-gunpowder story that sucked me in and kept me along for the ride until the last page. Also well worth your time.