Time -- Time zone popup 

pop up for time zone Setting

***   BACK END NOT WORKING YET ****
Look at

* https://github.com/openwebos/luna-sysservice/blob/master/Src/TimeZoneService.cpp#L93
* https://github.com/openwebos/luna-sysservice/blob/master/Src/TimePrefsHandler.cpp

If I find enough time I will write you some lines about how to use those API's

You can also look at the legacy apps and see how they deal with the timezone preferences.