'That diversion, though, cost him 6 months, and it meant he got to Russia in December, instead of summer.'
History doesn't agree with your statement.....the invasion
began in June instead of May.....which are Summer months
i believe not Winter months....& a delay of 1 month not 6.
"The occupation of Greece by the Axis Powers (Greek: Η Κατοχή, I Katochi, meaning "The Occupation") began in April 1941 after Fascist Italy and Nazi Germany invaded Greece, and lasted until Germany and its satellite Bulgaria withdrew from mainland Greece in October 1944. German garrisons remained in control of Crete and other Aegean islands until after the end of World War II, surrendering to the Allies in May and June 1945."
"Operation Barbarossa (German: Unternehmen Barbarossa) was the code name for Nazi Germany's invasion of the Soviet Union during World War II, which began on 22 June 1941."
"Hitler authorized an invasion of the Soviet Union on 18 December 1940 for a start date of 15 May 1941, but this was not met; instead, the invasion began on 22 June 1941."