It doesn't need that much time normally. That 3-4 week thing is a mind virus around here. It really depends on the beer, the yeast, the temp. A consistent hydrometer reading over a period of days and an FG that is close to what's expected is the only real way to know if it's done. If you want super clear beer, leave it for a couple of weeks. I get the same result in two days by cold-crashing my fermenter and have ** bottled moderately strong ales after 8 days in primary.
I'm still not clear. Do I wait for steady hydrometer reading before I move to the carboy, or before I bottle? If before I bottle, then when do I know I'm ready to transfer to the carboy?