Is it just after Googlebot crawled the page with link or rather after that page got to index?
1. Someone puts link on the website. Googlebot crawls that page with link. The site that is linked from crawled page gets boost in Google on specified anchor.
or
2. Someone puts link on the website. Googlebot crawls that page with link. Page gets to index after a few days. The site that is linked from crawled page gets boost in Google on specified anchor.
Ok, here we go. I have site that is about 3 years old. It hadn't been promoted since that time. It took almost 2 weeks since linking page till noticing a gain in SERPs. It seems that G. did a bulk backlink update, because my site went up for some other keywords.
Upon posting a content, or building links to your site, Google crawls them in a short period of time. Not simultaneous though, but sure they are crawled fast (based on the latest algorithm update).
The thing is, the updates as to when they will show up is unknown. So don't worry about indexing or crawling. It's Google's responsibility to crawl every link or page.
Now it depends upon the quality of a link, if the link is posted in a web directory that would take upto a month, but if it's posted in a news or any highly visited site, it's possible even in 1 - 3 hours.
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