tedster - 6:16 pm on Mar 27, 2011 (gmt 0)
This is a tough question to give a precise and tested answer for. So what I'm saying is a general impression based on working with a lot of sites, and I'm going to try to separate fact from impression.
Fact: A major reason for the new Caffeine infrastructure was to allow small amounts of crawl data to be integrated into the rankings very quickly - rather needing to wait and run recalculations only over large sections of the index at once.
Fact: Not everyone experiences a deep crawl at the same time - and it is not always once a month.
Impression: Full integration of backlink influence is extremely variable. It can be a couple days, and depending on trust, redirects etc it can take months. Some types of links (esepcially social media) seem to show their ranking influence almost immediately, but the value fades very rapidly, too.
Other types seem to grow over time - gaining power with age. And at a certain point, usually years, they start to fade in strength depending on the sites and pages involved, whether they stay active, how their own backlinks grow or vanish... too many factors for me to pin down with certainty.