How long between..

I just was wanting to know what seems to be the common timeframe between developing psoriasis and P Arthritis. I know it's a very good likely hood that I'm going to face this eventually, considering that my P is following the same path as my father's had. I know that for some it's as much as 20+ years, but, I just wanted to know what everyone's experiences were between diagnosis and P Arth developing?