I used kudzu for a while and did see an improvement in my ability to resist urges to drink. But I found that by doing the anti-candida diet, and the P&B shakes coupled with antifungals like forumula SF722 work much better than kudzu.
There are a few companies that make kudzu capsules & extracts, so just try one and see what happens. To answer your question about time of effectiveness, I think the stuff works immediately.
The best thing to do is to just start trying out these different remedies to find the one that works best for you. It's important to realize that these herbs, etc. are good for dealing with the --physical-- side of the addiction, but they're not a magic bullet -- they will only help you improve your chances of staying sober. For example, kudzu or anti-fungals won't get rid of a lousy family situation, or undo some bad abuse that might have happened to you at an earlier age. But they will significantly improve your chances to stay sober -- especially if you really want to.