Pre-colonial period

Myanmar did not have a standard time before the British colonial period. Each region kept its own local mean time, according to the Burmese calendar rules: sunrise, noon, sunset and midnight.^{[note 1]} The day was divided into eight 3-hour segments called baho (ဗဟို), or sixty 24-minute segments called nayi (နာရီ). Although the calendar consists of time units down to the millisecond level, the popular usage never extended beyond baho and at most nayi measurements; a gong was struck every nayi while a drum (စည်) and a large bell (ခေါင်းလောင်း) were struck to mark every baho.^[5]

Colonial period

The use of a common time began in British Burma in the late 19th century. The first confirmed mention of Rangoon Mean Time (RMT) at GMT+6:24:40^{[note 2]} being in use was in 1892,^[6] a year before the country's first time ball observatory^{[note 3]} was opened in Rangoon (Yangon) on 1 October 1893.^[7][8] However, the use of RMT as the common time, at least in some sectors, most probably started earlier. (The country's first rail service, between Rangoon and Prome (Pyay), began on 2 May 1877,^[9] and the non-authoritative IANA time zone database says RMT was introduced in 1880.^[10]) On 1 July 1905,^[11][12] a new standard time called Burma Standard Time (BST) at GMT+6:30—set to the longitude 97° 30' E, and 5 minutes and 20 seconds ahead of RMT—was first adopted by the Railways and Telegraph administrations.^[11][13] Although the rest of the country came to adopt BST, RMT continued to be used in the city of Rangoon at least to 1927.^{[note 4]} By 1930, however, BST apparently had been adopted in Rangoon as well.^{[note 5]}

The standard time was changed to Japan Standard Time (JST) during the Japanese occupation of the country (1942–1945) in World War II.^[14]

After independence

The standard time was reverted to GMT+6:30 after the war.^[14] It has remained ever since, even after the country's independence in 1948. The only change has been its name in English; the official English name has been changed to Myanmar Standard Time^[1] presumably since 1989 when the country's name in English was changed from Burma to Myanmar.^[15] The country does not observe a daylight saving time.^[2]