Well, Rich, frost here or there, wet is alone enough for me. Can't see much point in playing with cold wet clay. It will depend for everybody on their soil type, too, not just the local weather.
As for the original question, I don't even seem to know when Fletch put her cover down, but I really think there is nothing wrong with not weeding it beforehand, that's what it can be used for, to ease the weeding problem. It just needs to be in place for a long while, as per WG.