Fortunately I did get to it before you deleted it (found in the Mining Simulator of https://en.bitcoin.it/wiki/Mining).  It is a wonderful sample.  So I see that the date is included in the computation.  If that is accurate, then there will always be an answer.  So that also means that nonce does not make a huge difference and definitely there is no reason to retry skipped ones later on.

So is the Bits something that the pool changes or is that the difficulty level?