Extracting a time zone from a latitude longitude

Good Morning all, Having a look at the time zone functions in PHP you can enter a time zone city and get it's lat long. Does anybody know how you can run the function in reverse (or know of a similar function) i.e. get the time zone city from the geographic coordinates. Google maps was a thought but the functions are only for use in google maps which rules out my use for them. Have a great weekend. Cheers