C# Definition:

[StructLayout(LayoutKind.Sequential)]
private 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;

  public SYSTEMTIME( DateTime dt )
  {
    dt = dt.ToUniversalTime();  // SetSystemTime expects the SYSTEMTIME in UTC
    Year = (short)dt.Year;
    Month = (short)dt.Month;
    DayOfWeek = (short)dt.DayOfWeek;
    Day = (short)dt.Day;
    Hour = (short)dt.Hour;
    Minute = (short)dt.Minute;
    Second = (short)dt.Second;
    Milliseconds = (short)dt.Millisecond;
  }
}

VB Definition:

<StructLayout(LayoutKind.Sequential)> _
Private Structure SYSTEMTIME
   <MarshalAs(UnmanagedType.U2)> Public Year As Short
   <MarshalAs(UnmanagedType.U2)> Public Month As Short
   <MarshalAs(UnmanagedType.U2)> Public DayOfWeek As Short
   <MarshalAs(UnmanagedType.U2)> Public Day As Short
   <MarshalAs(UnmanagedType.U2)> Public Hour As Short
   <MarshalAs(UnmanagedType.U2)> Public Minute As Short
   <MarshalAs(UnmanagedType.U2)> Public Second As Short
   <MarshalAs(UnmanagedType.U2)> Public Milliseconds As Short
End Structure

Notes:

Sometimes, when trying to transform this struct into a CLR DateTime, I noticed that the year is 1 year behind. I don't know why.

Tips & Tricks:

Please add some!

C# Sample Class:

[StructLayout(LayoutKind.Sequential, Pack=2)]

internal 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 Milliseconds;

   public SystemTime(DateTime dt)
   {
      dt = dt.ToLocalTime();
      Year = Convert.ToUInt16(dt.Year);
      Month = Convert.ToUInt16(dt.Month);
      DayOfWeek = Convert.ToUInt16(dt.DayOfWeek);
      Day = Convert.ToUInt16(dt.Day);
      Hour = Convert.ToUInt16(dt.Hour);
      Minute = Convert.ToUInt16(dt.Minute);
      Second = Convert.ToUInt16(dt.Second);
      Milliseconds = Convert.ToUInt16(dt.Millisecond);
   }

   public SystemTime(ushort year, ushort month, ushort day, ushort hour = 0, ushort minute = 0, ushort second = 0, ushort millisecond = 0)
   {
      Year = year;
      Month = month;
      Day = day;
      Hour = hour;
      Minute = minute;
      Second = second;
      Milliseconds = millisecond;
      DayOfWeek = 0;
   }

   public static implicit operator DateTime(SystemTime st)
   {
      if (st.Year == 0 || st == MinValue)
     return DateTime.MinValue;
      if (st == MaxValue)
     return DateTime.MaxValue;
      return new DateTime(st.Year, st.Month, st.Day, st.Hour, st.Minute, st.Second, st.Milliseconds, DateTimeKind.Local);
   }

   public static bool operator ==(SystemTime s1, SystemTime s2)
   {
      return (s1.Year == s2.Year && s1.Month == s2.Month && s1.Day == s2.Day && s1.Hour == s2.Hour && s1.Minute == s2.Minute && s1.Second == s2.Second && s1.Milliseconds == s2.Milliseconds);
   }

   public static bool operator !=(SystemTime s1, SystemTime s2)
   {
      return !(s1 == s2);
   }

   public static readonly SystemTime MinValue, MaxValue;

   static SystemTime()
   {
      MinValue = new SystemTime(1601, 1, 1);
      MaxValue = new SystemTime(30827, 12, 31, 23, 59, 59, 999);
   }

   public override bool Equals(object obj)
   {
      if (obj is SystemTime)
     return ((SystemTime)obj) == this;
      return base.Equals(obj);
   }

   public override int GetHashCode()
   {
      return base.GetHashCode();
   }
}