America/Montevideo

Uruguay Uruguay wins the prize for the strangest peacetime manipulation of the rules. From Tim Parenti (2018-02-20), per Jeremie Bonjour (2018-01-31) and Michael Deckers (2018-02-20): ... At least they kept good records... Page 36 of Almanaque 2018, published by the Oceanography, Hydrography, and Meteorology Service of the Uruguayan Navy, seems to give many transitions with greater clarity than we've had before. It directly references many laws and decrees which are, in turn, referenced below. They can be viewed in the public archives of the Diario Oficial (in Spanish) at Ley No. 3920 of 1908-06-10 placed the determination of legal time under the auspices of the National Institute for the Prediction of Time. It is unclear exactly what offset was used during this period, though Ley No. 7200 of 1920-04-23 used the Observatory of the National Meteorological Institute in Montevideo (34° 54' 33" S, 56° 12' 45" W) as its reference meridian, retarding legal time by 15 minutes 9 seconds from 1920-04-30 24:00, resulting in UT-04. Assume the corresponding LMT of UT-03:44:51 (given on page 725 of the Proceedings of the Second Pan-American Scientific Congress, 1915-1916) was in use, and merely became official from 1908-06-10. Ley No. 7594 of 1923-06-28 specified legal time as Observatory time advanced by 44 minutes 51 seconds (UT-03) "from 30 September to 31 March", and by 14 minutes 51 seconds (UT-03:30) "the rest of the year"; a message from the National Council of Administration the same day, published directly below the law in the Diario Oficial, specified the first transition to be 1923-09-30 24:00. This effectively established standard time at UT-03:30 with 30 minutes DST. Assume transitions at 24:00 on the specified days until Ley No. 7919 of 1926-03-05 ended this arrangement, repealing all "laws and other provisions which oppose" it, resulting in year-round UT-03:30; a Resolución of 1926-03-11 puts the final transition at 1926-03-31 24:00, the same as it would have been under the previous law.