Function IstSommerzeit(zeit As Date, zone As TimeZoneInfo) As Boolean
    Return zone.IsDaylightSavingTime(zeit)
  End Function

' in Listbox eintragen:
ListBox1.Items.AddRange(TimeZoneInfo.GetSystemTimeZones.ToArray)
ListBox1.SelectedItem = TimeZoneInfo.Local
 
Private Sub ListBox1_SelectedIndexChanged(sender As Object, e As EventArgs) _
  Handles ListBox1.SelectedIndexChanged
  Dim zi As TimeZoneInfo = CType(ComboBox1.SelectedItem, TimeZoneInfo)
  Dim sz As Boolean = IstSommerzeit(Date.UtcNow, zi)
End Sub

 Public Function Sommerzeit(datum As DateTime) As Boolean
 
        'Gibt True zurück falls es sich um ein Datum in der Sommerzeit der 
        ' Zeitzone "Berlin" handelt
 
        Dim zz_berlin As TimeZoneInfo = Nothing
        Dim zz_alle As New ArrayList
        zz_alle.AddRange(TimeZoneInfo.GetSystemTimeZones.ToArray)
 
        For Each it In zz_alle
            If it.ToString.Contains("Berlin") Then zz_berlin = it
        Next
 
        Return zz_berlin.IsDaylightSavingTime(datum)
 
    End Function