I can only talk from my perspective... When I played the game for the first time a few years ago it took me around 10 months from start to "finish" and I think none of the harem stuff (maybe the home harem, but not 100% sure) was implemented back then... (with the new content since then I would think that it takes at least two months or more todo everything)
Of course using the wiki some time could be saved, but going blind and without cheats into a normal New Game takes some time. (at least it did for me... ^^)
Hard to say those are the only requirements to trigger it: