Not sure if the four pages of posts have answered your original question adequately, but I will give an answer from my experience. When I started, I asked the same question. (I wanted to know when I could realistically expect to quit my day-job.)
The answer I heard most was, "About 6 months." That's how long it took the people in my circle to hit the primary goal of replacing their day-job income. I was warned it would take work and lots of perseverance, and it did. But they were right. It took six months. The best part was, that was just the initial goal. Having learned so much during those first six months, it was clear that the second six months would see growth from that original milemarker.