Automatic Option Missing from the Time Menu

The required Time Zone Map files to automatically update the time are most likely missing from the device's software if your device doesn't provide the option to automatically set the time. 

In order for the Automatic option to be enabled on the device, go to the Support Center and enter the product name or the serial number of your device. Once your device is selected, select Other and search for “Updating Automotive Maps and Software with Garmin Express".  Follow the instructions in that FAQ to update the software on your device.  Check for optional updates and select the item named Time Zone Map.

Once the Time Zone Map has been downloaded, the device will be able to automatically set the time.