If the Greeks hadn't invaded anywhere, as I think your scenario is asking, then there would be an earlier Barbarossa. As winter would come later, the Germans might even take Moscow. Or maybe not, it depends, but I think we'd see a further German advance. I don't think the Nazis would win, personally. But it's possible. At the very least it lengthens the war.
well, preparations and weather for barbarossa mean that you can start 4 weeks earlier, so you have 4 "good" weeks more...
also, 4 weeks less air war with uk means lesser losses... this improve german air force...
but 4 weeks more aren´t enough to beat russia - maybe leningrad fall (this would improve german position, but not enough to "win"), moscow could fall, but the germans couldn´t hold it
the winter is still very cold and an unpleasent surprise for the germans, even if i agree that 4 weeks more war before winter means 4 weeks more heavy russian losses, so less russians can counterattack
but also more germans will be lost in this 4 weeks... it is an interesting plot... also the consequences in other areas...