There are time zones (actually more than 24). They have names like Atlantic Standard Time. They are offset from GMT as + or - so many hours. MST is GMT -7, for example.

There is NO information in the api or the locale data that knows what city is in what time zone. All the PC knows is that it is set to GMT+9. It doesn't care if the PC is in Kamchatka or Adelaide.

www.planetsourcecode.com has some examples and data sets that do current time lookups in like 150 of the world's biggest cities. You can expand the database to include cities you need. I am assuming this is what you really mean.