I think your choice of the "general" is the key point here. Yes, these are general times, and for a novice running relatively small doses, they will work perfectly for timing PCT. But we all have to remember that when you start is based as much on dose as it is on half-life. For instance, a guy running two grams of test e each week may have to wait 10-14 days longer than a guy running 500mgs test e.
I don't know anyone who runs 2 grams of test each week and then attempts to recover their natural endogenous test levels, lol. For the number of guys still running a PCT (however few that may be now, haha) You can almost judge it by feel after awhile. My last few cycles I have finished up with a smaller dose of prop (300mg EW) for 2-3 weeks after my last long ester pin so that I could keep some semblance of balance leading up to PCT. After the last shot of prop you don't even need to wait a week, more like 3 days.
Also, starting a bit early has been debated before....but it dose work for soem people. The BEST way to know is to get blood tests done immediately following your last pin. Say your levels are at 2000 and you're running test E only. With the half life of 5-6 days or so after 2 to 2.5 weeks the levels should be rouughly 250. However, you have to start the time after the peak of the last injection, which will be a couple days. So, 3 weeks seems like a better figure. Doc Scally has a wonderful write up on this that I will find at some point today. It discusses HPTA restart and how full suppression and low levels before PCT aid in a quicker recovery. Also, during the last few weeks before PCT I'm a huge fan of blasting HCG or HMG, whether you have atrophy or not. HCG should not be used during PCT because it "mimics" a hormone and is exogenous...in turn causing further suppression of endogenous testosterone. I'm also a believer in his theory that Nolva and Clomid combined work far greater than one or the other by itself.
It's funny that you mention "breaking out" on Clomid. I could swear I break out with acne more on PCT drugs than any amount of exogenous test or any other AAS for that matter. It seems weird but I guess breaking out is a good sign of your natural test recovering.