the Google PR that we can see in our toolbars is actually On Google cache servers. The true PR of the page is never distributed in real time. the PR On Google cache servers used to be updated every few months but lately it has been a bit random. But as the other person said don't worry about your PR. Concentrate on building your site and look at your site rankings. In the end knowing your PR isn't going to change your search engine ranks, PR is a distraction that most of us are guilty of in the beginning
I can't reply any much better though it will be a distraction for most webmasters especially when a part of your revenue depends on it. Many online companies still refer to PR as a parameter in determining quality site. Heck, this fake PR6 site even sold for a high amount mostly due to its PR6 eventhough it was fake.
Pssst... TOP SECRET! Somebody at Google told me that PR is updated when there is full moon on a Friday the 13th...
Google employees say that PR updation is regular and gradual process There are no defined dates for this update. You can see a change in your PR when your web pages deserves it. Why are you concerned with this update when Google itself is less concerned with it.
I have created the same thread a the google topic....users say it depend from backlink...and there is no fixed border
Dont worry about pr i would like to have a site with 25k users a day with a pr1 compared to a pr6 site with 500 users a day but thats just me.
There are lots of thing worth worrying about rather than "when will PR update?". I would be better if you focused on things that matters.