To view an example of this feature, please read this knowledge base article.
This dialog appears when you click edit... on the extra tab of the ribbon. It allows you to define time zone sets, which can be associated with sample lists in order to identify the time zones where contacts live, based on their telephone numbers. Each time zone set contains a table of dialing codes, matching them with their associated time zones. To use a time zone set in conjunction with a contact list, specify the list in the numbers tab of the sample list properties.

The following options are available:
Add: Allows you to add a time zone set. The edit time zone set dialog appears. You can also right-click the list and select add....
Edit: Allows you to edit the details of the selected time zone set. The edit time zone set dialog appears. You can also right-click an item in the list and select edit....
Delete: Removes the selected time zone set. You can also right-click an item in the list and select delete, or press DEL.
This dialog appears when you add a new time zone set, or edit an existing one. It allows you to edit the details of the set, and define the time zones within the set. Each set contains one or more dialing codes and their associated time zones.

The following options are available:
prefix column, enter the dialing code, and in the time zone column, enter the associated time zone. For example, you might enter 33 in the prefix column, and France in the time zone column.