I have talked to IFBB pros that have endorsement contracts with major supps companies that say they don't take more than 6 weeks off before hopping back on, they said usually 4 weeks and your receptors are clear and its ok to jump back on. Now I also have talked to guys that compete on the national level, not pros, that say they are off cycle when they only run 750mg of test per week. I never really go in depth with them about PCT, whether they ran it or if they considered it time on or off, but some had given advice to use it starting last week of cycle and continuing for 3 weeks.
I have run PCT starting last week and going for 6 weeks and for 3 weeks and I never really noticed to drastic of a difference between the two except for the 3 weeks longer length. My balls came back nice and full and I retained a good amount of my gains both way, so I stick with 3 weeks after and pct complete. I did go cold turkey a couple of times because I ended up having to have surgery both times and I didn't have time to prepare for pct so I just came off with no time for anything and it sucked, I lost everything and got fat, but that may have been from not being able to move for 8+months. I wont ever come off cold turkey again. I will always use pct.