Japan's Longest Day
The film depicts the 24 hours from noon on August 14, 1945 (Showa 20), when the Showa Emperor and cabinet ministers decided to surrender at an Imperial Conference, to noon on August 15, when the acceptance of the Potsdam Declaration was announced to the public via the radio broadcast of the Emperor's Jewel Voice (Gyokuon-hoso) through NHK.
Source: cinematokyo.com · Tokyo mini-theater & independent cinema showtimes.