You can quickly and easily get to the clock settings by tapping the current time at the top of your screen.
In theory, making sure the box that is labeled "GPS time" is checked will ensure that the time changes automatically as you leave one time zone and enter another. I currently live nowhere near a time zone line, so I don't really ever get to play with this function or try it out myself. But that's how it
should work.
@BOBNARIZONA – you may be encountering issues with it because Arizona does not observe daylight savings... they are on standard time year-round. So you may experience it changing when it shouldn't and not changing when it should, depending on which borders you are crossing and the time of year you're doing it. For example, if you cross from Arizona to California (or back) between November and March, it should perform as expected and move the clock appropriately. However, if you made that same trip in the summer, it would theoretically move the clock even though you wouldn't want that to happen, because in the summer MST and PDT are the same. In that case, the car recognizes you're going from one time zone to another, but doesn't recognize Arizona's oddball situation. Crossing from Arizona to New Mexico should never result in a change as far as the car is concerned, because you aren't changing time zones (both states are in the mountain time zone). However, during the summer months, the time is different between them because NM changes to MDT whereas AZ stays in MST and is an hour behind.
As an aside for people who are checking out the clock settings for the first time and live somewhere that does observe daylight savings, take this as an opportunity to make sure you're set up correctly. Right now, since we are in daylight time part of the year, you should have the box checked in your clock settings that says "daylight saving time." In November, when the clocks change, all you have to do is go back in here and uncheck that box. That will change your time back one hour. In the spring, you go back in and recheck that same box to change it forward one hour.