I'm not sure you mean PageRank? PageRank is the old score Google gives pages and while it influences your position in the search results, it's only one factor. Google even downplays it these days.
I think from you phrase "I had one hub drop to the third page" that you are talking about SERP position, ie Search Engine Results Page position. That is to say where your hub appears on the Google results pages for any particular search phrase. Is that right?
If so, then the answer is that your result will change every day now. Google now adjusts the results roughly every 24 hours. Now, more often than not, your results will stay roughly the same, but it's not uncommon to bounce up and down places between pages even. It will all be affected by your content, when it was updated, inbound links, etc and all these factors are then in play on your competition too, so hence there's fairly fluid movement.
Bear in mind also that my SERP on a phrase might not be the same as yours on the same phrase, as others things like geography can affect search results.
Editing pages to make them more attuned to a phrase or phrases that people search on makes sense, but then it's best to step back. Constantly editing, especially titles, (if it's very regular tweaking, ie daily, rather than more natural updating) can also negatively impact Google SERP placement.
Hope that helps.