Most high quality backlinks will appear in your account within 3 days after they appear on the internet. In some cases it can take as long as a month.
The biggest factor that determines how long it takes is the quality of the link. For example, links that are on orphan pages might never be found. Orphan pages are pages with no backlinks. Since no one links to orphan pages, it's hard for any web crawler to find it (including Google). This might especially be relevant if you are dealing with negative SEO.