Porto Velho time zone history
Daylight saving time was used in 4 years since 1970, last in 1988; under the current rules the clocks no longer change. On standard time, clocks in Porto Velho run 16 minutes ahead of local mean solar time.
UTC−4
Standard time is UTC−4 all year under the current rules.
Summer time in 4 of 57 years since 1970
Before 1970
Standard time changes
| Date | Change | New standard time | Clock label |
|---|---|---|---|
| Before 1970 | |||
| January 1, 1914 | Local mean time (UTC−4:15:36) replaced | UTC−4 | numeric only |
Daylight saving periods
| Years | Clocks go forward | Clocks go back | Shift and labels |
|---|---|---|---|
| 1931 | October 3 | not that year | 1 hour |
| 1932 | October 3 | April 1 | 1 hour |
| 1933 | not that year | April 1 | 1 hour |
| 1949 | December 1 | not that year | 1 hour |
| 1950 | December 1 | April 16 | 1 hour |
| 1951–1952 | 1 December, 00:00 | 1 April, 00:00 | 1 hour |
| 1953 | not that year | March 1 | 1 hour |
| 1963 | December 9 | not that year | 1 hour |
| 1964 | not that year | March 1 | 1 hour |
| 1965 | January 31, December 1 | April 1 | 1 hour |
| 1966–1967 | 1 November, 00:00 | 1 March, 01:00 | 1 hour |
| 1968 | not that year | March 1 | 1 hour |
Since 1970: the periods shared by 4 of 16 zones, listed on the Brazil page.
Also on UTC−4
Manaus (Brazil), Bolivia, Cuiabá (Brazil), Boa Vista (Brazil), Campo Grande (Brazil), Guyana, Venezuela, Barbados, Martinique and Santiago (Chile) (nearest first; 8 more on the list of offsets).
Clocks next door since 1970
- Rio Branco (448 km): usually 1 hour behind; different on 1,965 days in 1985–1988 and 2008–2013.
- Eirunepé (698 km): usually 1 hour behind; different on 2,091 days in 1985–1988, 1993, 1994 and 2008–2013.
- Manaus (759 km): same time except 126 days in 1993 and 1994.
- Bolivia (976 km): same time except 350 days in 1985–1988.
- Cuiabá (1,138 km): same time except 3,671 days in 1988–2019.
How it compares
Standard time has stayed at UTC−4 since 1914.