Make sure the links are are on high importance sites that get multiple daily updates, and so will get multiple visits by search bots daily. Ideally, ensure they are on the home page of that site, or one page down. Places like national newspaper sites, top blogs and similar.

Use BacklinksIndexer easily index backlinks on search engines

If you chuck them on a low quality site with thin content, buried half a dozen steps down the path tree, it might take weeks - or even never, if it’s been flagged a a site used for link spam.