(From an Apple Knowledge Base article)
In the United States, the state of Indiana observes Daylight Saving Time (DST) for the first time in many counties on April 2, 2006 (02-April-2006). Some counties in Indiana also change from the Eastern to Central time zone. This article explains how to adjust your Mac for these changes.
Note: If you live in an Indiana county that observed Daylight Saving Time before 2006, no changes are necessary.
If you live in an Indiana county that changes from Eastern to Central time as of April 2, 2006:
Use Date & Time preferences to choose a Central time zone city, such as Chicago, on or after 02-April-2006.
If you live in an Indiana county that is not changing to Central time and has not observed DST before:
Your steps depend on which version of Mac OS X you are using.
Mac OS X 10.4 or later
Download and install the Mac OS X 10.4.5 Update, or later. This contains updated Daylight Saving Time rules to automatically maintain the proper time.
Mac OS X 10.3.9 or earlier
Use Date & Time preferences to choose an Eastern time zone city, such as Detroit, on or after 02-April-2006.
