Vietnam time zone belongs to UTC +7:00. This time zone is also applied for Laos, Thailand, Cambodia, Indonesia, Russia, and western of Mongol. The time zone of Vietnam is seven hours ahead of Greenwich Meantime and Coordinated Universal Time. In 1998, Vietnam referenced ISO 8601 and created its own standard. After the construction of Phu Dien Observatory, all areas in French Indochina including Northern Vietnam (Tonkin), Central of Vietnam (Annam), Southern Vietnam (Cochinchina), along with Cambodia, Laos and Guangzhouwan of China) were located in 104°17’17”E longitude time zone from 00:00 01 July 1906 onward. From 1911 to 1940, the time zone GMT+ 0 (the solar time of Greenwich) was adopted as an official time of the region by Metropolitan France. Yet, French Indochina observed GMT+ 7 from 00:00 01 May 1911.
After that, the time zone of French Indochina was followed by a change in time zone of Vichy authorities. Owing to the change, French Indochina was integrated to GMT +8, skipping 60 minutes at 23:00 31 December 1942. When French Indochina was completely occupied by Japan, the region followed the time zone of Tokyo (GMT+9), skipping 60 minutes at 23:00 14 March 1945. By August Revolution in Vietnam (1945), the Empire of Vietnam fell, and the Declaration of Independence of the Democratic Republic of Vietnam was announced. Provisional Uniform Government of the Democratic Republic of Vietnam took control, and GMT +7 was chosen as official time zone in Vietnam on 02 September 1945. Meanwhile, such regions which were attacked as Laos and Cambodia adopted GMT+ 8; and non-attacked areas used GMT +7. Southern Vietnam also chose GMT +7 from 00:00 01 July 1955 under State of Vietnam’s rule. However, Southern Vietnam local time was changed to GMT +8 from 23:00 01 January 01 1960, skipping 60 minutes; while, Northern Vietnam still remained its official UTC+7 from 01 January 1968. After the Fall of Saigon in 1975, all territory of Vietnam chose UTC +7 as official local time.
Vietnam local time expresses the identity of the country. It is said that the geographical position of a country on the globe has a tight association with the time zone passing the country. If a country has its territory stretching on many time zones, it can choose a standard time zone among other zones go set up its local time. The territory of Vietnam is located completely in the time zone of UTC +7, thus the Vietnam standard time is UTC +7. The time zone is also related to the practiced customs in Vietnam. Local time in Vietnam has great differences in time zone to other countries in the region and in the world, except Laos, Cambodia, Thailand, and Mongolia. For example, Vietnam is 12 hours ahead of USA. That means when it is 6:00 am (morning) in Washington DC USA, it is 6:00 pm in Hanoi Vietnam. Vietnam and China is seen to have the same longitude, but Vietnam time zone is fast. The following table will show more detail about time zone of Vietnam in comparison with other countries in the region and across the world.