Damn now i'm confused, i thought it was 2weeks too 
The basis behind PCT, among other things, is to combat unopposed estrogen in the system after cycle completion. Those compounds with longer 1/2-lives will persist longer in your system after completion of your cycle, so you still have elevated levels of circulating exogenous (synthetic) testosterone in your system. Those compounds with shorter 1/2-lives, like test prop, clear rapidly, leaving you exposed to the effects of unopposed estrogen.
I will typically switch to test prop for the last 4 weeks of my cycle, to allow all the other compounds to clear, while still maintaining relatively (albeit synthetically) high test levels. My PCT begins, then, the day after my last shot of test prop.
