Gow long does PR Take

My case: just finished buiding a website, got lucky and bought 2 active domains that the owners didn't renew 1 PR7 1PR4 . The PR4 is very active but the guy didn't have any more time nor interest to run it. If I do do follow links to the main page how long would it take to my website to rank at least 3?
thanks

cant even type the title well

PR updates 4 time a year.

Next PR update :

Third Page Rank Update: 30th September 2010 - 31st October 2010

(as found on the internet)

One thing to remember about PR that Google folks have mentioned several times - while the "public" page rank is updated sporadically, the true backend page rank is calculated as close to real-time as possible.