The routes are I think 13 chapters each. You'll need a guide to get the endings and I recommend getting both the sweet ending and the flashback ending. (The bad ending isn't that interesting in most cases, although it is in the last route.) But you could also just play through it once and then watch the other ending on youtube. There are 5 routes total and I strongly recommend doing them in order. In theory you could read a route in a day if you are a fast reader and have nothing else to do.

Maybe it'll come back on Story Jar, but that seems to be free-to-play, and it would be excruciating to get through Demon's Bond half a chapter at a time. I'd still do it though.