Consider the following timestamp: 1995-07-14T13:05:00.0000000-03:00.
When asked what the -03:00 at the end is called, many developers answer, “a time zone.”
The -03:00 does represent the offset from UTC.
To get the UTC time, invert the offset sign then add it to the time such as 13:05 + 3 = 16:05 in UTC.
Okay, following this ok now more details..
The mistake is in thinking that the offset is all there is to a time zone. Nope. A time zone is a geographical area, and it consists of many pieces of information, such as
- One or more offsets. (DST is a thing, after all.)
- The dates when DST transitions happen. (These can and do change whenever governments feel like it.)
- The amount of time applied when transitions happened. (It’s not one hour everywhere.)
- The historical records of changes to the above rules.
In short, is is not possible to establish the time zone by the offset!