it depends on when the site you are linking from gets crawled. so you neeed to make the engines crawl that site to find your link. you do this by pinging the page or SBMing the page
Its all about quality and most importantly relevancy. No point in building backlinks continuously unless its from high PR traffic triggering sites.
Hey, Ive noticed a few things with my sites and backlinking and would like other peoples experiences. I note that when I build backlinks, I may get a very very small initial boost, however it seems that I dont get the full effect of the backlinks until they are registered in my webmaster account... Then after they have been registered, they tend to appear in the Google 'link:' operator.
Google do back link update in every 2 or 3 months. Then it will count all your back links which are relevant. If you want to check your back links then Google webmaster tool will help you find out the total number of back links you have. Another one is Link:www.yoursite.com, you can type this on google search box. But this will return only quality back links.
When Google cache your link page after this back links effect. So keep in mind that put links on good cache link pages.