I think it took me about 6 months, but that's because I only had a few hubs and didn't really know what I was doing at first.
As soon as I started treating HP like a part-time job (and worked on it daily), I instantly got traffic and a $180 payout (my first payout.)
Since then it's gone up and down depending on how active I am. I've been getting a payout every month for years now, but during long periods of inactivity the drop in traffic is noticeable.
Hubs need to be constantly updated, tweaked, and improved.