Anyone tell me after how much days Google update page ranks...and also tell me how much backlinks need for PR 4
I think pr is not very important but what is important is the SERP. and for tha you need both quality link and quality content.
Google is constantly reevaluating PR, they typically however only update the tool bar once per quarter.
The page rank updation happens normally after every 3 months, but it also gets delayed many a times. Only google knows when to update Rank.