It can take that long to reach full effect but it doesn't just come BAM! You usually start feeling a slight positive effect after 6-7 weeks.

Because of that it feels like you shouldn't have to wait more than 6 weeks or so. By 9 weeks if you haven't felt anything positive it's not going to happen, at least not on that dosage. If you had felt a slight improvement, then waiting a little more to keep dosages down would have made sense.