google does not have fixed schedule for updating page rank. Frequency of posting, and quality plus quantity of backlinks are very important factor. Try to post everyday, and make comments in every blog you can find to get backlinks. You can make sure the blogs have at least PR1, and allow "dofollow" comments.
A single link will do PR is not all about link, you also need to create useful and quality content for your site.
Google updates all websites page rank every 3 months or before 3 months. The next expected PR update then will be on the last week of January 2010.
I think it is every three months. manny07 shouldn't that be the first week? Maybe I misread this somewhere...
Google generally update its page 3-4 times in year. But its last 4-5 PR updates were very quick 45 to 60 days gap between the updates