Huh... it's very relative. It depends on your reading speed, the mode you play, if you're a completionist (counters, achievements, buildings, girls' levels, etc)... I wouldn't know. +25h? To say something, as long as you don't play easy mode, obv.
If you entertain yourself long enough, the whole intro alone can be +1h. Right now there are about +30 quests in total (+ all the girls' tasks), and only a few of them are short, the rest have a "logical" duration so to speak.