Being 'well known' is relative. I have a pretty good reputation on this forum and a few others, but there are lots of forums that have never heard of me! I wouldn't worry about being well known anywhere. I answer posts on this forum (and others) to share the things I have learned as I have grown my business and I ask questions to learn the things I DON'T know. The end result is that I have a fairly solid presence in several industries simply by being involved with them.
As far as a time line goes, it would all depend on how much time you spend and how much interaction you have in various places, whether they be online forums, face-to-face networking, or blogs, newsletters, print articles, etc. There is no cut and dried answer to that.
We recently had to change doctors, after 12 years with the same one. The hubby and I found a possible new doctor through a combination of the phone book and online searches and then scheduled a 'meet and greet' appointment. The doctor had the personality of a wet dishrag, no bedside manner, and was rude about the fact that there was nothing wrong with us to explain our visit! Needless to say, we kept on looking and found another doctor, this time through 'word of mouth', that we really like and get along with well.
After meeting our second potential family doctor (the one we liked) we asked several people if they were familiar with the first doctor we met. Talk about bad impressions! We heard nothing but negative things about the first doctor from our previous doctor's office staff, the guys at the ER (F-I-L fell in shower and we had to get him checked out), and from several other sources, including some of my co-workers. On the other hand, we heard an amazing amount of positive things about the new doc! The point about this is that had we started by asking people we knew for suggestions or if they knew someone’s reputation, we could have possibly avoided the first disappointing appointment (and the co-pay

).
The moral of the story? Socializing, networking, being involved, and getting to know people on a personal basis is, in my opinion, critical for getting an excellent reputation and becoming ‘well known.’ The more you interact, the farther your influence and reputation will spread.