Seems like 5-6 months is a normal interval for a high quality single developer VN for larger updates. Eternum is in scope much smaller game and the last update was from February with the next being projected for late July or early August. For PC the two developers spit the next update in half to be able to have an earlier release with the first half and those are actually two guys working on it and not one.
DPC has a very high production quality, I mean in what other VN do you have a scene like you had during the contest in Ep. 9 with what...50 or so characters on screen? All in unique costumes, most of them have a name and at least some form of characterization as in "the player kinda knows them", with around...20 or so being very fleshed out characters...yeah, he takes his sweet time, but he also delivers the quality in my opinion. Sure, 9 months really is a stretch but there is no real way to make larger updates in less than half a year I think.