I cant accept this because I registered a site before 2 months and it got PR,.. it doesn't applies to your concept!!
To determine the snapshot date. Find a very popular blog/website that posts very often (daily). Check all the posts and see when the PR stops appearing. Do that to maybe two or three blogs and you have the date figured out.
Im not waiting for any update for my page rank anymore. I am mainly focused in getting traffic right now. But who knows if what Google really thinks, maybe they'll give importance to site's traffic as well when giving pr?
None of my new sites got PR, but the older ones did got it. It may be an old PR update which is not upto date for sure. For instance one of my site which is new has 16k backlinks has a PR1, while one site which has 5 backlinks has a PR2, which is really unimaginable.