I just started week 5 of a Test C 12 week plan. Noticeable gains started beginning of week 4. It's my understanding that it's not 4-6 weeks for Test to kick in, it's just that long for Blood levels to stabilize. Taking 2-3 weeks off means it's just that much longer for you to get your blood levels stable for optimum growth.
Just this 4th of July weekend, I took my gear along to make sure I didn't miss my Monday morning pin.
I feel that following a strict dosing schedule is just as important as nutrition, Rest, and your time hitting the weights.