Repeatedly: E.g. the battle of France took six weeks, and the 2003 invasion of Iraq just over a month, never mind things like the Warsaw Pact invasion of Czechoslovakia that was over in 2 days. However, occupation can be a bitch...
Nazi Germany and Soviet Russia took Poland in 37 days (people forget that the Soviets and Nazis were allied at the beginning of WWII and had an agreement to split Poland). The Nazis alone took Netherlands in four days, and Belgium in 18 days.