Mac OS X 10.6: Setting the date and time
You can set your computer’s date and time manually or have the date and time set automatically using a network time server.
Important:You must specify your time zone whether the date and time are set manually or automatically. If you don’t specify the time zone, your clock may show the wrong time and the time stamp on emails and files may be incorrect.
To set the date and time:
Choose Apple menu > System Preferences, click Date & Time, and then click Date & Time.
Set the date and time. For more information about the options, click the Help button (looks like a question mark).
Click Time Zone, and select your city.