well for this topic i cant tell you when google update PR but usually they make update every 3-4 month maybe for me google update their pagerank in last of this month or first of september thanks,
Ya generally it is said that Google updates the prs in every six months so the last update was in April...Hope next month Google update it..Eagerly waiting for the update...
I think only Google knows that. I'd say don't worry about it, just build backlinks and you'll surely get your PR when that happens.
There is no certain date for updates. Just focus on the SEO, when you do the job well you will see the results no not to see it in the way of a good pagerank..
This is very common question and it has just 2 answers - Google PR updation average time is 3 months and the answer number 2 is Google knows the exact date. Don't worry you can expect it in every 3-4 months.