Change system date programmatically

A lot of great viewpoints and approaches are already here, but here are some specifications that are currently left out and that I feel might trip up and confuse some people.

1. On Windows Vista, 7, 8 OS this will require a UAC Prompt in order to obtain the necessary administrative rights to successfully execute the SetSystemTime function. The reason is that calling process needs the SE_SYSTEMTIME_NAME privilege.
2. The SetSystemTime function is expecting a SYSTEMTIME struct in coordinated universal time (UTC). It will not work as desired otherwise.

Depending on where/ how you are getting your DateTime values, it might be best to play it safe and use ToUniversalTime() before setting the corresponding values in the SYSTEMTIME struct.

Code example:

DateTime tempDateTime = GetDateTimeFromSomeService();
DateTime dateTime = tempDateTime.ToUniversalTime();

SYSTEMTIME st = new SYSTEMTIME();
// All of these must be short
st.wYear = (short)dateTime.Year;
st.wMonth = (short)dateTime.Month;
st.wDay = (short)dateTime.Day;
st.wHour = (short)dateTime.Hour;
st.wMinute = (short)dateTime.Minute;
st.wSecond = (short)dateTime.Second;

// invoke the SetSystemTime method now
SetSystemTime(ref st); 

You can use a call to a DOS command but the invoke of the function in the windows dll is a better way to do it.

public struct SystemTime
{
    public ushort Year;
    public ushort Month;
    public ushort DayOfWeek;
    public ushort Day;
    public ushort Hour;
    public ushort Minute;
    public ushort Second;
    public ushort Millisecond;
};

[DllImport("kernel32.dll", EntryPoint = "GetSystemTime", SetLastError = true)]
public extern static void Win32GetSystemTime(ref SystemTime sysTime);

[DllImport("kernel32.dll", EntryPoint = "SetSystemTime", SetLastError = true)]
public extern static bool Win32SetSystemTime(ref SystemTime sysTime);

private void button1_Click(object sender, EventArgs e)
{
    // Set system date and time
    SystemTime updatedTime = new SystemTime();
    updatedTime.Year = (ushort)2009;
    updatedTime.Month = (ushort)3;
    updatedTime.Day = (ushort)16;
    updatedTime.Hour = (ushort)10;
    updatedTime.Minute = (ushort)0;
    updatedTime.Second = (ushort)0;
    // Call the unmanaged function that sets the new date and time instantly
    Win32SetSystemTime(ref updatedTime);
}  

Use this function to change the time of system (tested in window 8)

 void setDate(string dateInYourSystemFormat)
    {
        var proc = new System.Diagnostics.ProcessStartInfo();
        proc.UseShellExecute = true;
        proc.WorkingDirectory = @"C:\Windows\System32";
        proc.CreateNoWindow = true;
        proc.FileName = @"C:\Windows\System32\cmd.exe";
        proc.Verb = "runas";
        proc.Arguments = "/C date " + dateInYourSystemFormat;
        try
        {
            System.Diagnostics.Process.Start(proc);
        }
        catch
        {
            MessageBox.Show("Error to change time of your system");
            Application.ExitThread();
        }
    }
void setTime(string timeInYourSystemFormat)
    {
        var proc = new System.Diagnostics.ProcessStartInfo();
        proc.UseShellExecute = true;
        proc.WorkingDirectory = @"C:\Windows\System32";
        proc.CreateNoWindow = true;
        proc.FileName = @"C:\Windows\System32\cmd.exe";
        proc.Verb = "runas";
        proc.Arguments = "/C time " + timeInYourSystemFormat;
        try
        {
            System.Diagnostics.Process.Start(proc);
        }
        catch
        {
            MessageBox.Show("Error to change time of your system");
            Application.ExitThread();
        }
    }

Example: Call in load method of form setDate("5-6-92"); setTime("2:4:5 AM");

Here is where I found the answer.; I have reposted it here to improve clarity.

Define this structure:

[StructLayout(LayoutKind.Sequential)]
public struct SYSTEMTIME
{
    public short wYear;
    public short wMonth;
    public short wDayOfWeek;
    public short wDay;
    public short wHour;
    public short wMinute;
    public short wSecond;
    public short wMilliseconds;
}

Add the following extern method to your class:

[DllImport("kernel32.dll", SetLastError = true)]
public static extern bool SetSystemTime(ref SYSTEMTIME st);

Then call the method with an instance of your struct like this:

SYSTEMTIME st = new SYSTEMTIME();
st.wYear = 2009; // must be short
st.wMonth = 1;
st.wDay = 1;
st.wHour = 0;
st.wMinute = 0;
st.wSecond = 0;

SetSystemTime(ref st); // invoke this method.