May 19, 2011
1:51 a.m.
It seems necessary to split North Vietnam and South Vietnam into two zones for timezone history between 1967 and 1975/1976 I have found corroboration that North Vietnam went from UTC+8 to UTC+7 on August 8, 1967, while South Vietnam stayed on UTC+8 'until after the end of the Vietnam war'. Saigon fell end of April 1975. Source: http://en.wikipedia.org/wiki/T%E1%BA%BFt There is another reference, discussing the difference between North and South Vietnam timezone in 1968, http://www.math.nus.edu.sg/aslaksen/calendar/cal.pdf on page 29. The timezone difference led to a different date for the Tet festival in that year, creating confusion about the starting data for the Vietcong's Tet offensive.