The Uruguayan government has decided NOT observe daylight savings time from July 2015.
So if you’re coming here from Argentina there’s no need to change your time display as there was previously.
However a number of other South American countries observe daylight saving time, so if you are coming to Uruguay from one of our South American neighbours, check the time, especially if you bought your travel tickets in advance.
Brazil (except for equatorial Brazil) observes DST. So if you are coming from Rio or Sao Paulo, there will be a time difference but not if you are coming from Salvador, Fortaleza or other cities in the north.
Uruguay observed DST from 2006 to early 2015. In the second half of 2015, the government has decided to put an end to daylight savings following pressure from the restaurant sector (link in Spanish).
Argentina dabbled with DST but currently does not observe it.
Chile appears to vary when it adjusts the hour year by year (Chileans, please correct me if I am wrong).