From OpenStreetMap Wiki
|boundary = timezone|
|Boundaries of time zone|
|Used on these elements|
|Tools for this tag|
boundary=timezone is used to tag regions that observes a uniform standard time. Such boundaries could be used for automatic adjustment of clock time during the travel using current GPS coordinates, for example.
- Name of the time zone could be specified by name=* (Central European Time, Moscow Time, Pacific Time Zone...)
- For abbreviation code for time zone use ref=*, e.g. ref=AST for Atlantic Standart Time Zone, ref=CET for Central European Time etc.
- Use utc=* to tag Coordinated Universal Time offset of the time zone in ±hh:mm format, e.g. utc=+01:00 for Central European Time, utc=-07:00 for Mountain Time Zone etc.