I have been re reading The Rise and Fall of the Third Reich, and as luck would have it I made my way through the chapter on Barbarossa. I had forgotten another interesting point that bears directly on this discussion. The German Army was actually poised to make the push on Moscow earlier than they did. I had forgotten that Hitler had ordered, much against the loud objections of his generals, ordered them to halt on Moscow and instead push towards Leningrad and Stalingrad because he wanted to secure those important industrial and agricultural areas before moving on to Moscow. In his mind he felt denying Moscow this important area was going to deal them a big blow. Frankly, by this point his megalomania was in full gear and despite what his much more strategy minded generals told him he made them go along with his orders. Eventually the push to Moscow was started up again, but by then it had delayed them long enough for the autumn rains to start mud season, which quickly turned into the harsh winter.
So, having remembered this little bit of information it is clear that the delay with Yugoslavia was only one in a string of very bad decisions made about operation Barbarossa. Frankly, if Hitler had just decided to cut his losses and postpone Barbarossa until the following late springtime while all the while keeping the facade of god relations with Russia it would have been an interesting situation in which America enters the war with Britain, but Russia, up until Germany would have invaded, would not become part of the Allies, and if the Germans could have actually completed the ruin of Russia it would have left America and Britain on their own. Though to be fair to the Russians, they fought like cornered rattlesnakes with lasers on their heads. It is a good bet they would have really really hurt the Germans very badly even in defeat allowing perhaps America and Britain to still eventually pull of their invasions of the various fronts. As Shirer wrote in his book, the Germans grossly misjudged the Russian military strength when they kept having new division after new division appear out of nowhere and start attacking them.