[Vigilanteman]

You are correct. The Soviet Union declared war on Japan about 5 minutes before midnight on August 8 and launched first offensive operations at 2 minutes after midnight on August 9. So there was less than ten minutes between the declaration of war and the opening of hostilities.

The Japanese gave us more warning (by several hours) on Pearl Harbor.

[Joe 6-pack]

Yep...it’s interesting to look at participants of the Potsdam Conference (which included the Soviets) and the Potsdam Declaration/Ultimatum which was issued to Japan. The Soviets did not sign on to the ultimatum whose only signatories were the US, Great Britain and Chiang Kai Shek’s China.