Hitler had never planned to invade Russia in the winter.
The invasion was planned in the spring of that year, but had to be delayed for several months due to the situation in Romania and Greece.
Since Germany had no oil of her own, she needed to secure the oil wells in Romania, but England threatened those by invading Crete and Greece.
So Germany had to clear this threat first, which caused the massive delay.
BTW, how many did know that when the invasion started, the German army ran into a Russian army, which was geared up in attack mode.
Russia had planned to overrun Europe in the summer of that year, which was clearly proven by the fact that the Russian army was equipped for advancing attack warfare tactics and Germany did not encounter a defensive army, trying to protect Russia.
A further proof was the fact, that the KGB opened several secret files, clearly stating that Russia was poised to defeat Europe by attacking that spring with its huge panzer army.
So in a way Hitler saved Europe from becoming communist satellite states.