David Patte has released a free time zone tool that uses the Olson Time Zone database (same database that the Terran Atlas already uses):

http://www.relativedata.com/time-zone-master

You might want to check it out... It is important to cross reference various sources like this to other astrological atlases for the sake of accuracy. I've stated that the Olson time zone database is the best because it is maintained by about 500 people from around the world and therefore will have fewer errors because of the number of people cross checking the data.