Two more pieces of information about historical timezone changes in Iran, this time in the late 1970s: I just ran into an academic paper that looks into the psychology of daylight savings in Iran, and it has the exact times for the change in 1977 and the beginning of the change in 1979 (but not its end, unfortunately). https://www.jstor.org/stable/178704 Here's the quotes from the paper: 1. '"Iran's official time keeper moved the clock one hour forward as from March 22, 1977 (Farvardin 2, 2536) to make maximum use of daylight and save in energy consumption. Thus Iran joined such other countries as Britain in observing what is known as 'daylight saving.' The proposal was originally put forward by the Ministry of Energy, in no way having any influence on observing religious ceremonies. Moving time one hour forward in summer means that at 11:00 o'clock on March 21, the official time was set as midnight March 22. Then September 24 will actually begin one hour later than the end of September 23 [...]." Iran's time base thus continued to be Greenwich Mean Time plus three and one-half hours (plus four and one-half hours in summer).' The article sources this from Iran Almanac and Book of Facts, 1977, Tehran: Echo of Iran, which is on Google Books at https://www.google.com/books/edition/Iran_Almanac_and_Book_of_Facts/9ybVAAAA.... (I confirmed it by searching for snippets.) 2. "After the fall of the shah, the revolutionary government returned to daylight-saving time (DST) on 26 May 1979." This seems to have been announced just one day in advance, on 25 May 1979. The change in 1977 clearly seems to be the first daylight savings effort in Iran. But the article doesn't mention what happened in 1978 (which was still during the shah's government), or how things continued in 1979 onwards (which was during the Islamic Republic). This data doesn't seem to match tzdata: First, an entry for 1977 needs to be added, for which we seem to have complete data. Second, the beginning of daylight saving time in 1979 needs to be changed to May 26. Thanks, Roozbeh