Choose “Mail, Contacts, Calendars,” and under Calendar tap “New Invitation Alerts” to turn it on.
Choose “Mail, Contacts, Calendars” > Sync, then choose a period of time.
Choose “Mail, Contacts, Calendars” > Time Zone Support, then turn Time Zone Support on. Select a time zone for calendars by tapping Time Zone and entering the name of a major city.
When Time Zone Support is on, Calendar displays event dates and times in the time zone of the city you selected. When Time Zone Support is off, Calendar displays events in the time zone of your current location as determined by the network time.
IMPORTANT: Some carriers don’t support network time in all locations. If you’re traveling, iPhone may not display events or sound alerts at the correct local time. To manually set the correct time, see Date and Time.