How long does it take for SEO to work?

It's can't say like this becouse don't think you are only one who is doing SEO your competator also doing SEO so if your competator do more SEO then you they will get profit more and in short time you will not gat any more difference but at lest with in 1-2 months you can see some good result of you do hardwork

 

It's depends on quality of your links and your truly fresh content if your back links comes from high PR sites which has less number of out bound links like less then 20 out bound links so it's would be more banishment for you. and it's could ranked your key words higher in major Search Engines.

 

Depending on how competitive the terms are that your going after...2-3 months before you should worry.

 

The link can get effect very fast, you know that in SEO contest, website will be up and down every hour or even minute, this mean link will be effect in SEO very fast once google index the link.

 

I don't know how old your site is but SERP rankings can fluctuate wildly with young sites (less than a year old). Plus, there are so many other factors beyond shear back link numbers that come into play for anyone to give you a definitive answer. Domain trust and domain authority not only for your site but also for the sites linking to you can be huge. Check out SEOmoz's site regarding domain trust and authority, I believe they have a video. It will help explain inbound linking factors better.