为什么 SetSystemTime() 在下午表现不同？

我编写了以下类来更改系统日期时间，但我不明白为什么它在一天中的不同时间运行不同：

• 早晨：传递到的确切时间SetTime()被设置为系统时间。
• 下午：传递给SetTime()+1Hr的时间被设置为系统时间，额外的一小时从哪里来？

.

public class SystemDateTimeController
{        

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


    private struct SYSTEMTIME
    {
        public ushort wYear;
        public ushort wMonth;
        public ushort wDayOfWeek;
        public ushort wDay;
        public ushort wHour;
        public ushort wMinute;
        public ushort wSecond;
        public ushort wMilliseconds;
    }

    public static void SetTime(DateTime NewDateTime)
    {
        try
        {
            SYSTEMTIME systime = new SYSTEMTIME();

            systime.wMilliseconds = (ushort)NewDateTime.Millisecond;
            systime.wSecond = (ushort)NewDateTime.Second;
            systime.wMinute = (ushort)NewDateTime.Minute;
            systime.wHour = (ushort)NewDateTime.Hour;

            systime.wDayOfWeek = (ushort)NewDateTime.DayOfWeek;

            systime.wDay = (ushort)NewDateTime.Day;
            systime.wMonth = (ushort)NewDateTime.Month;
            systime.wYear = (ushort)NewDateTime.Year;

            Win32SetSystemTime(ref systime);
        }
        catch (Exception e)
        {
            Log("Failed to set system date time to: " + NewDateTime.ToString() + ". Exception: " + e.ToString());
        }

    }

}

我知道传递给SetTime()和测试目的的确切时间，并消除与源有关的任何可能性，我什至传递了一个硬编码字符串：Convert.ToDateTime("07/06/2018 13:00:00");