Short answers, pulled from the story.
The Hirohito surrender broadcast was made at noon Japan Standard Time on the 15th of August 1945. The recording itself was made at the Tokyo Imperial Palace on the night of the 14th of August 1945, between 11:25 p.m. and 11:30 p.m.
Hirohito decided to speak directly to the nation because he knew a written rescript alone would not be enough to convince the military to accept surrender. His advisor Marquis Koichi Kido had also warned him of the risk of a military coup if the decision was not communicated with the emperor's personal authority.
No. The word "surrender" was not used in the broadcast. The speech stated that the Japanese government had accepted the "joint declaration" of the United States, Great Britain, China, and the Soviet Union, referring to the Potsdam Declaration. A radio announcer clarified the meaning after the speech concluded.
The broadcast was delivered in formal Classical Japanese, with pronunciation unfamiliar to ordinary Japanese. The speech made no direct reference to surrender, and the poor audio quality of the phonograph recording added to the confusion. Many listeners did not recognize that Japan had capitulated until a radio announcer explained it afterward.
Yes. As many as 1,000 officers and soldiers raided the Imperial Palace on the evening of the 14th of August 1945, searching for the recordings. Major Kenji Hatanaka also led soldiers to the NHK station in the early hours of August 15, where an officer threatened announcer Morio Tateno at gunpoint. The coup was suppressed by the Eastern District Army.
Hirohito described the atomic bomb as a "new and most cruel bomb" whose power to cause damage was "incalculable, taking the toll of many innocent lives." He stated that continued fighting would lead to the total extinction of human civilization, citing the bomb as a reason for accepting the Allied declaration.