How often are "Links to Your Site" updated in the Google Webmaster tool?
I found this thread with various replies on the matter, from "every few days" and "around 20 to 30 days" to "backlinks to my website that were removed 9 months ago". That doesn't really help much.
Are there some more precise sources? A blog post of some SEO company that did some research on this? Even some information put out there by Google?