One of the most common questions people ask about positive affirmations is this: "How long does it take for an affirmation to work?" Unfortunately, this is a question no one can answer with accuracy. It depends on what you're trying to accomplish, what your personal blocks are, how determined you are, etc. It's not like following the directions to make a pie, which has specific ingredients and a set baking time.
Let's say your goal is to become a millionaire. There are lots of ways to go about it (Bill Gates and Michael Jordan took very different paths that led to success!), but it's safe to assume that it's going to take quite a while before you achieve this goal--especially if you're unemployed and don't have a strong network.
If your goal is to lose 100 pounds, it's not going to happen in a month... and if it does, you're doing something horribly wrong. After all, no one puts on that much weight overnight: It's a gradual process years in the making. Consequently, it's going to be at least MONTHS to safely take all the weight off.
Same thing if you're trying to quit smoking. Some people like my grandfather have amazing willpower and can quit cold turkey. Most people have to struggle for months or even years to overcome their addiction. Affirmations can help when correctly used, but they won't give you instant results.
On the other hand, sometimes people notice immediate changes when they start using daily affirmations. Someone trying to boost his self esteem might feel better after repeating a meaningful "self confidence" affirmation a few times. But if he's really down on himself and has years of psychological damage to undo, it might take longer.