If you speed ran everything (skipping all dialogue) I would wager you could do everything in about 4 or 5 hours. If you read all dialogue you're looking at more like 12+ hours. (I haven't timed it myself, I can only go based off of saves).
To give some other metrics. There are currently 7 characters in the game with fully completed progressions (level 0 to 5), 2 with half completed progressions (level 0 to 3) and 1 yet to be (re)added to the game. There are 145 scenes accessible in the memory room and if my counting is correct 80+ unique animations to view (all sex scenes). By the end of the next major update there will be 10 characters with full progressions in the game bringing up to just over 100+ unique animations I believe.
After that the update will be the overall main story which will add a tonne of new scenes with different characters (demons/creature girls) as well. We are about 80% completed total.