If you need to change your time zone, the time displayed your existing appointments, include all day appointments, will reflect the new time zone. To avoid problems, you should follow these steps before changing the time zone:

1. Export your calendar to CSV or Excel format.
2. Create a new calendar folder and move the existing items to it (use any table view and select all, copy or drag to the new folder.)
3. Change the time zone.
4. Import the file into Outlook.

Once you are sure everything is correct, delete the calendar folder containing the original items.