Программно устанавливаем дату и время

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)
{
  
    SystemTime updatedTime = new SystemTime();
    updatedTime.Year = (ushort)2011;//Год
    updatedTime.Month = (ushort)7;//Минуты
    updatedTime.Day = (ushort)11;//День
 
    updatedTime.Hour = (ushort)15; //Час
    updatedTime.Minute = (ushort)0;//Минуты
    updatedTime.Second = (ushort)0;//Секунды
  
    Win32SetSystemTime(ref updatedTime);    
    SystemTime currTime = new SystemTime();
    Win32GetSystemTime(ref currTime);
}