What I couldn't find was any reference in the National "BoletÃn Oficial" where Federal Laws and Decrees are published... my guess is that there is sufficient "hearsay" so that the Provinces are officialy "taking sides", but only that... all national info I could see was in the media and not on official sites
There is only some info 12/03/09 (not specific for provinces) from Ministerio de Defensa as No. 26.350: "In fulfillment of the Naval Observatory Buenos Aires (Onbaa) with the community, as established by law No. 26.350, the third Sunday in March of 2009 at 00:00 pm, going back one hour on the spindle 3 west of Greenwich. This means that at 00:00 pm the 15th of March 2009, will be 23:00 pm the previous day. " http://www.hidro.gov.ar/Noticias/RENoticias.asp?idnot=197 or http://www.worldtimezone.com/dst_news/dst_news_argentina06.html Alexander Krivenyshev, World Time Zone