By default Evolution uses the system-wide time zone. This can be changed under EditPreferencesCalendar and TasksGeneralTimeTime zone.

If you deal a lot with people in another specific time zone you can display that second time zone in the day view of the calendar. You can set a second time zone under EditPreferencesCalendar and TasksGeneralTimeSecond zone.

You can also configure time zone information specific to each appointment. To do that, add a new or edit an existing appointment and click the globe button to customize the time zone that the time exists in. For example, if you live in New York but have a telephone meeting set for noon with someone in California, you need to make sure that your schedules are coordinated. Setting time zones on a per-appointment basis helps avoid that potential confusion.