Google updates all of the visible pageranks at the same time. If you publish a page two days before the
PR update, it will show
PR in two days. If you publish two months before the update, it will take two months.
Really though, I wouldn't worry too much about
PR unless it is suddenly dropping to zero. There are hundreds of other ranking factors that go in to search results, and
PR is just one - an outdated one at that!