TheCloudlessSky's answer works for windows XP: starting with Vista the function to call is SetDynamicTimeZoneInformation, otherwise "Your current time zone is not recognized. Please select a valid time zone using the link below." will be shown until the next reboot.
Bonus: calling SetDynamicTimeZoneInformation makes it unnecessary to manually edit the registry, and so it won't be necessary to start the program as administrator.
Here is TheCloudlessSky's snippet modified to work on Vista and higher
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using Microsoft.Win32;
namespace TimeZoneTest
{
[StructLayoutAttribute(LayoutKind.Sequential)]
public struct SystemTime
{
[MarshalAs(UnmanagedType.U2)]
public short Year;
[MarshalAs(UnmanagedType.U2)]
public short Month;
[MarshalAs(UnmanagedType.U2)]
public short DayOfWeek;
[MarshalAs(UnmanagedType.U2)]
public short Day;
[MarshalAs(UnmanagedType.U2)]
public short Hour;
[MarshalAs(UnmanagedType.U2)]
public short Minute;
[MarshalAs(UnmanagedType.U2)]
public short Second;
[MarshalAs(UnmanagedType.U2)]
public short Milliseconds;
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct TimeZoneInformation
{
[MarshalAs(UnmanagedType.I4)]
public int Bias;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 0x20)]
public string StandardName;
public SystemTime StandardDate;
[MarshalAs(UnmanagedType.I4)]
public int StandardBias;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 0x20)]
public string DaylightName;
public SystemTime DaylightDate;
[MarshalAs(UnmanagedType.I4)]
public int DaylightBias;
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct DynamicTimeZoneInformation
{
public int Bias;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
public string StandardName;
public SystemTime StandardDate;
public int StandardBias;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
public string DaylightName;
public SystemTime DaylightDate;
public int DaylightBias;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
public string TimeZoneKeyName;
[MarshalAs(UnmanagedType.U1)]
public bool DynamicDaylightTimeDisabled;
}
[StructLayout(LayoutKind.Sequential)]
public struct RegistryTimeZoneInformation
{
[MarshalAs(UnmanagedType.I4)]
public int Bias;
[MarshalAs(UnmanagedType.I4)]
public int StandardBias;
[MarshalAs(UnmanagedType.I4)]
public int DaylightBias;
public SystemTime StandardDate;
public SystemTime DaylightDate;
public RegistryTimeZoneInformation(TimeZoneInformation tzi)
{
this.Bias = tzi.Bias;
this.StandardDate = tzi.StandardDate;
this.StandardBias = tzi.StandardBias;
this.DaylightDate = tzi.DaylightDate;
this.DaylightBias = tzi.DaylightBias;
}
public RegistryTimeZoneInformation(byte[] bytes)
{
if ((bytes == null) || (bytes.Length != 0x2c))
{
throw new ArgumentException("Argument_InvalidREG_TZI_FORMAT");
}
this.Bias = BitConverter.ToInt32(bytes, 0);
this.StandardBias = BitConverter.ToInt32(bytes, 4);
this.DaylightBias = BitConverter.ToInt32(bytes, 8);
this.StandardDate.Year = BitConverter.ToInt16(bytes, 12);
this.StandardDate.Month = BitConverter.ToInt16(bytes, 14);
this.StandardDate.DayOfWeek = BitConverter.ToInt16(bytes, 0x10);
this.StandardDate.Day = BitConverter.ToInt16(bytes, 0x12);
this.StandardDate.Hour = BitConverter.ToInt16(bytes, 20);
this.StandardDate.Minute = BitConverter.ToInt16(bytes, 0x16);
this.StandardDate.Second = BitConverter.ToInt16(bytes, 0x18);
this.StandardDate.Milliseconds = BitConverter.ToInt16(bytes, 0x1a);
this.DaylightDate.Year = BitConverter.ToInt16(bytes, 0x1c);
this.DaylightDate.Month = BitConverter.ToInt16(bytes, 30);
this.DaylightDate.DayOfWeek = BitConverter.ToInt16(bytes, 0x20);
this.DaylightDate.Day = BitConverter.ToInt16(bytes, 0x22);
this.DaylightDate.Hour = BitConverter.ToInt16(bytes, 0x24);
this.DaylightDate.Minute = BitConverter.ToInt16(bytes, 0x26);
this.DaylightDate.Second = BitConverter.ToInt16(bytes, 40);
this.DaylightDate.Milliseconds = BitConverter.ToInt16(bytes, 0x2a);
}
}
public class TokenPrivilegesAccess
{
[DllImport("advapi32.dll", CharSet = CharSet.Auto)]
public static extern int OpenProcessToken(int ProcessHandle, int DesiredAccess,
ref int tokenhandle);
[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
public static extern int GetCurrentProcess();
[DllImport("advapi32.dll", CharSet = CharSet.Auto)]
public static extern int LookupPrivilegeValue(string lpsystemname, string lpname,
[MarshalAs(UnmanagedType.Struct)] ref LUID lpLuid);
[DllImport("advapi32.dll", CharSet = CharSet.Auto)]
public static extern int AdjustTokenPrivileges(int tokenhandle, int disableprivs,
[MarshalAs(UnmanagedType.Struct)]ref TOKEN_PRIVILEGE Newstate, int bufferlength,
int PreivousState, int Returnlength);
public const int TOKEN_ASSIGN_PRIMARY = 0x00000001;
public const int TOKEN_DUPLICATE = 0x00000002;
public const int TOKEN_IMPERSONATE = 0x00000004;
public const int TOKEN_QUERY = 0x00000008;
public const int TOKEN_QUERY_SOURCE = 0x00000010;
public const int TOKEN_ADJUST_PRIVILEGES = 0x00000020;
public const int TOKEN_ADJUST_GROUPS = 0x00000040;
public const int TOKEN_ADJUST_DEFAULT = 0x00000080;
public const UInt32 SE_PRIVILEGE_ENABLED_BY_DEFAULT = 0x00000001;
public const UInt32 SE_PRIVILEGE_ENABLED = 0x00000002;
public const UInt32 SE_PRIVILEGE_REMOVED = 0x00000004;
public const UInt32 SE_PRIVILEGE_USED_FOR_ACCESS = 0x80000000;
public static bool EnablePrivilege(string privilege)
{
try
{
int token = 0;
int retVal = 0;
TOKEN_PRIVILEGE TP = new TOKEN_PRIVILEGE();
LUID LD = new LUID();
retVal = OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, ref token);
retVal = LookupPrivilegeValue(null, privilege, ref LD);
TP.PrivilegeCount = 1;
var luidAndAtt = new LUID_AND_ATTRIBUTES();
luidAndAtt.Attributes = SE_PRIVILEGE_ENABLED;
luidAndAtt.Luid = LD;
TP.Privilege = luidAndAtt;
retVal = AdjustTokenPrivileges(token, 0, ref TP, 1024, 0, 0);
return true;
}
catch
{
return false;
}
}
public static bool DisablePrivilege(string privilege)
{
try
{
int token = 0;
int retVal = 0;
TOKEN_PRIVILEGE TP = new TOKEN_PRIVILEGE();
LUID LD = new LUID();
retVal = OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, ref token);
retVal = LookupPrivilegeValue(null, privilege, ref LD);
TP.PrivilegeCount = 1;
// TP.Attributes should be none (not set) to disable privilege
var luidAndAtt = new LUID_AND_ATTRIBUTES();
luidAndAtt.Luid = LD;
TP.Privilege = luidAndAtt;
retVal = AdjustTokenPrivileges(token, 0, ref TP, 1024, 0, 0);
return true;
}
catch
{
return false;
}
}
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct LUID
{
internal uint LowPart;
internal uint HighPart;
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct LUID_AND_ATTRIBUTES
{
internal LUID Luid;
internal uint Attributes;
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct TOKEN_PRIVILEGE
{
internal uint PrivilegeCount;
internal LUID_AND_ATTRIBUTES Privilege;
}
public class Program
{
public const int ERROR_ACCESS_DENIED = 0x005;
public const int CORSEC_E_MISSING_STRONGNAME = -2146233317;
[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
private static extern bool SetTimeZoneInformation([In] ref TimeZoneInformation lpTimeZoneInformation);
[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
private static extern bool SetDynamicTimeZoneInformation([In] ref DynamicTimeZoneInformation lpTimeZoneInformation);
public static void Main(string[] args)
{
var regTimeZones = Registry.LocalMachine.OpenSubKey("SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones");
// Print out all the possible time-zones.
//foreach(var subKey in regTimeZones.GetSubKeyNames())
//{
// Console.WriteLine(subKey);
//}
var subKey = regTimeZones.GetSubKeyNames().Where(s => s == "Atlantic Standard Time").First();
string daylightName = (string)regTimeZones.OpenSubKey(subKey).GetValue("Dlt");
string standardName = (string)regTimeZones.OpenSubKey(subKey).GetValue("Std");
byte[] tzi = (byte[])regTimeZones.OpenSubKey(subKey).GetValue("TZI");
var regTzi = new RegistryTimeZoneInformation(tzi);
TokenPrivilegesAccess.EnablePrivilege("SeTimeZonePrivilege");
bool didSet;
if (Environment.OSVersion.Version.Major < 6)
{
var tz = new TimeZoneInformation();
tz.Bias = regTzi.Bias;
tz.DaylightBias = regTzi.DaylightBias;
tz.StandardBias = regTzi.StandardBias;
tz.DaylightDate = regTzi.DaylightDate;
tz.StandardDate = regTzi.StandardDate;
tz.DaylightName = daylightName;
tz.StandardName = standardName;
didSet = Program.SetTimeZoneInformation(ref tz);
}
else
{
var tz = new DynamicTimeZoneInformation();
tz.Bias = regTzi.Bias;
tz.DaylightBias = regTzi.DaylightBias;
tz.StandardBias = regTzi.StandardBias;
tz.DaylightDate = regTzi.DaylightDate;
tz.StandardDate = regTzi.StandardDate;
tz.DaylightName = daylightName;
tz.StandardName = standardName;
tz.TimeZoneKeyName = subKey;
tz.DynamicDaylightTimeDisabled = false;
didSet = Program.SetDynamicTimeZoneInformation(ref tz);
}
int lastError = Marshal.GetLastWin32Error();
TokenPrivilegesAccess.DisablePrivilege("SeTimeZonePrivilege");
if (didSet)
{
Console.WriteLine("Success, TimeZone Set!");
}
else
{
if (lastError == Program.ERROR_ACCESS_DENIED)
{
Console.WriteLine("Error: Access denied... Try running application as administrator.");
}
else if (lastError == Program.CORSEC_E_MISSING_STRONGNAME)
{
Console.WriteLine("Error: Application is not signed ... Right click the project > Signing > Check 'Sign the assembly'.");
}
else
{
Console.WriteLine("Win32Error: " + lastError + "\nHRESULT: " + Marshal.GetHRForLastWin32Error());
}
}
Console.ReadLine();
}
}
}