Does PageRank flow happen instantaneously or over time?

Which way is it?

[joshbuckley]

I have a website with a PR 3. The highest site in my category is PR4. I just received a link from a friend's site (PR 7) homepage. There are just 20 or so links on his homepage, so there should've been at least PR 5 "flow" to my site (by the way, other links from his homepage seem to have appropriate PR flow).

Now, Google has already indexed the new version of his homepage with my link (I can see it in cache), but I'm not seeing any benefit from that. I was in 5-th position in SERPs and I'm still there.

So, my question is, does PR flow happen instantaneously or is it done over time? Also, his homepage is on totally different topic than my site. Would that "hinder" PR flow? By the way, neither of our sites have any penalties as much as we know.

[tedster]

The real PageRank value that Google uses in private to calculate rankings is updated continually, and it's calculated to many decimal places. Because PR is only one of many factors used in calculating the SERPs, your ranking may not change from the effect of a new link or two on your real PR.

There's more information here: Google PR - PageRank FAQs [webmasterworld.com]