I've created a file called GMT.reg with the following content: [-HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation] [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation] "Bias"=dword:00000000 "StandardName"="GMT Standard Time" "StandardBias"=dword:00000000 "StandardStart"=hex:00,00,0a,00,05,00,02,00,00,00,00,00,00,00,00,00 "DaylightName"="GMT Standard Time" "DaylightBias"=dword:00000000 "DaylightStart"=hex:00,00,0a,00,05,00,02,00,00,00,00,00,00,00,00,00 "ActiveTimeBias"=dword:00000000 "DisableAutoDaylightTimeSet"=dword:00000001 I'm calling this from cmdlines.txt during the install but it's not sticking. After the first logon, opening the time zone windows still has the checkbox ticked. However, if I run GMT.reg again the checkbox is cleared, but the time is not thrown 1 hour back as expected. So right timezone, but wrong time