Section 5.2.4 "When"

[Michael Douglass <mikeadouglass@gmail.com>]

The use of a UTC offset and UTC values is very problematic.

Timezone rules change frequently in many parts of the world and this can 
make it very difficult if not impossible to determine what local time an 
event occurred if insufficient information is stored.

As a quick summary take a look at 
https://devguide.calconnect.org/Time-Zones/Best-Practices/