I have been looking for the info for an hour or more but I can't really find the old posts.
In any case, beyond possible suppression, there is really no reason to start w/cort blockers before week 3. The body doesn't begin to react negatively to the weird hormonal imbalance/flux that occurs when coming off for 2 or 3 weeks. At that point the HPTA is starting to come back but the flood exogenous hormones are now gone causing the body to say WTF and produce more cort.
Again, I don't claim to be an expert and I just trying to spur the discussion. Hopefully, one of the more knowledgeable members will chime in, but I'm not holding my breath because it seems that a good number of them don't stop in/post in here anymore.