on the PU front
PUs in the case of beer, wort etc etc, are about the liquid, and the liquid being microbiologically stable. They aren't what you need to concern yourself with when you are filling an NC cube. The liquid you are filling your cube with has in fact had thousands of PU's already and is almost certainly as sterile as its ever going to get - you boiled it for an hour!!
So, worrying about PUs in the cube is pointless. What you need to worry about there, is sterilising the interior surface of the cube, sterilising anything you have in there like hops, hop bag etc.
You need enough time and temp, for the heat to not only kill the things on the surface, but also for the heat to penetrate any cracks, scratches, crevises (the threads on your tap if you have one fitted) and kill microbes in there, and you need to assume that its more or less going to be dry heat that has to do the trick, because its entirely possible that surface tension is keeping actual liquid out of fine scratches in the plastic.
Surface sterilisation and dry heat sterilisation are entirely different beasts to pasteurisation and the numbers aren't quite the same.
in the brewing industry, or at least the bit of it I am familiar with, we would conduct a hot water sterilisation at 80+C for 20 minutes or a hot caustic CIP at a little lower (the caustic provides some chemical back up to the heat) - and thats just to sanitise a fermenter etc.... Thats probably "more" than sufficient, but remember, for the purposes of NC, you want something much closer to sterile because you have no yeast to help control any bacterial growth, so you need no bacteria at all, not just less of them.
Now, No-Chill obviously does a sufficient job in most cases, but people still do get infected cubes - so its plainly not so far in advance of the requirements that you can afford to be careless. The hotter you can get your wort into the cube and the longer it stays hot - the safer you are.
That doesn't mean that you will get an infection, or even that the risk is particularly high if you do this stuff a few degrees cooler. But it is more risk - and for me, personally, if I wasn't pretty sure that the liquid temperature in my NC cube wasn't at or close to 80C for at least 15 or so minutes after I filled it, i would consider it too much risk.
Your tolerance for risk may well be different to mine though, so YMMV.
TB