Well, I'm biased about this topic since I believe I was the first to write about it (certainly not the first to do it) back in the Dan Duchaine days. It was the Steroids For Health 3 week cycle. (Later adopted as the 2 week cycle and the bridged cycle and the every other wek cycle and every other bull shite version).
Yes, it's easier to keep a 10 pound gain than a 20 pound gain. That's just basic biophysics.
As far as the "kicking in' period, I can't believe that myth still exists. Steroids put you in an anabolic state almost immediately. Of course, it takes time to grow muscle. But it's not like your body needs to wait a few weeks. Muscle growth actually comes in pretty quick spurts. You probably won't "see" results until a week or two but that doesn't mean the process hasn't begun.
Steroids actually becoem less effective after a couple of months. You'll continue to gain but the best and most solid growth period should be in the first month.