From my experiments I would say that new backlinks take at least three or four months to affect the SERPS of google and yahoo - does that sound about the same as other people experience? I guess there is a link aging process to combat spam, seems logical, but it makes it a long wait to see the results of your labor!
* Backlinks will be count on google almost instantly but full advantage will be from time to time, let’s say that 20% instantly
* Google treat backlinks with age as well. If you have backlinks older than your competitors that will be more important to Google.
* Google also depends on the competition of your niche. If you got a high competitive niche it will take more time than No-Competitive niche. That will for sure control the spammers sites.