Recently I changed my site improving the title
and description
metatags of many pages. Looking at Webmaster Tools I saw that Googlebot already crawled the new contents (and also found duplicate titles I promptly fixed), but the search results pages still have the old descriptions and titles.
Is it know how much time is needed by Google to update the SERPs? In your experience, is it something happening really fast or really slow, supposing a rule to exist?