To automatically set the time zone during a Windows 7 installation you will need to add the following component to your Autounattend.xml file or the sysprep unattend.xml file.
<component name="Microsoft-Windows-Shell-Setup" processorArchitecture="x86" publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS" xmlns:wcm="http://schemas.microsoft.com/WMIConfig/2002/State" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<TimeZone>Tasmania Standard Time</TimeZone>
</component>