how long will it takes backlinks to be listed in google?also can anyone suggests some good blogs to post comment?
Yes, it depends upon the PR as well as traffic on that website. High PR websites like Digg, Diigo crawl the page in just minutes.
If you have a blog yourself, it's good to post at CommentLuv-enabled blogs. Go search for CommentLuv blogs in your field: http://comluv.com
If your link is from good PR site which has good traffic and good will, than these link may crawl in an hour. Google is best place to find free resource.
I think,it depends on the website PR and traffic.If your link is from good PR then this link may crawl within few hours.Thanks!