I think I asked that question once in one of the "ask us anything" thread : when do you start to consider a client a "regular" and I got so many different answers. Seems like there isn't an agreed upon benchmark, and that's normal.
I don't really have "a" regular myself, but maybe a few SPs I see in rotation. But right now I'm back into a more exploratory phase where I want to meet new people.
As far as I'm concerned, I think once or twice a month over maybe a bit more than 6 months starts to become a regular thing. I've only been hobbying for 2 years or so anyway.