When did Denmark get invaded?

At 04:20 (am) April 9, 1940, German soldiers who had been hiding in a ship in Copenhagen port started the Copenhagen part of the invasion of Denmark. Their aim was to take over the Danish military headquarters in the nearby Citadel. Around the same time German troops cross the German-Danish border at the southern part of Denmark, paratroopers landed at crucial air fields, and troops landed at the strategic habour of Korsør.

The main "persuasive argument" for at quick surrender was, however, the bombers flying over Copenhagen accompanied by the treat that the city would be bombed (Rotterdam-style), if the Danish government didn't accept that "German military took over the defence of neutral Denmark gainst a possible British attack" - so the Danish government accept under protest, and stayed in power for three years into the WW2 in spite of the German occupation - a very unusual set-up compared to other occupied European countries.