If you are talking about a PR update, I do not think that they reveal that information.

Today in fact.

Google updates their algorithms daily. I think last year they did something like 500 tweaks to the algorithm.

Most updates go unmentioned, because they go unnoticed by all but a few people.

Only major changes like the Caffeine update in January 2010 and the May Day update in May of 2010 attract any real attention these days.



p.s. If you are talking about the PR update, they usually do that about every four months, usually implementing in January, May and September. But I have heard rumor that they are either slowing or stopping PR updates on the Google toolbar.

Google is constantly tweaking their algo, periodically they'll update the Google toolbar but they are constantly assessing backlinks.

Next PR update =

If you absolutely NEED to know the PageRank of a page, it's pretty easy to estimate by just looking into the backlink profile. Just filter out all nofollow links, and sort by highest PR. The PR of that site will usually be the highest PR dofollow link it has.