If your calendar is messed up due to not using the correct ‘Use DST’ setting, or from changing time zones, the usual fix is to export the calendar to Excel or CSV format while the time zone is configured so the appointment times are correct. Then change the time zone settings on the computer, move the existing appointments to a new calendar folder and import the appointments from the spreadsheet or CSV file. Once you are satisfied the appointments all imported correctly you can delete the backup calendar. (To create a new folder, go to File, New folder… select Calendar as the folder contains type and the Calendar folder as the new location.)
The new automated method when you change time zones is the Time Zone update tool. This tools works with all versions of Outlook and is an updated version of the tool included in Outlook 2007.
Microsoft Office Outlook Tool: Time Zone Data Update Tool for Microsoft Office Outlook
Published March 10, 2008. Last updated on June 22, 2012.