Doug is a truck driver and wants to know if there's a program that will automatically change the time zones that he's in. Leo says it should happen automatically based on his IP address. Apple's OS X provides that feature, which just has to be turned on. But there are third party programs like Time Traveler and TimeSync Tool that will do it as well.
There's also this conversation - http://superuser.com/questions/284532/automatically-change-time-based-on-current-location