This may help you. This part is a sample of my WINNT.SIF which changes all my regional settings to English - Australia. It also correctly specifies my timezone to 255 A.U.S. Eastern Standard Time (GMT+10:00) Canberra, Melbourne, Sydney [RegionalSettings] LanguageGroup=1 UserLocale=00000c09 InputLocale=0c09:00000409 InputLocale_DefaultUser=0c09:00000409 SystemLocale=0c09 UserLocale=0c09 UserLocale_DefaultUser=0c09 My Timezone is 255 A.U.S. Eastern Standard Time (GMT+10:00) Canberra, Melbourne, Sydney This is a sample of my settings of the Gui Unattended Section. [GuiUnattended] AdminPassword="" EncryptedAdminPassword=NO OEMSkipRegional=1 TimeZone=255 OemSkipWelcome=1 First of all, during setup, I still got presented with the GMT-8 timezone, even though you can clearly see that I have defined it differently: Timezone=110