Public Sub qqq()
    Dim c As Range, r As Range, t#
    ComboBox1.Clear
    t = Timer
    Set r = Range([c2], [c1000])
    For Each c In r
        If Len(c.Value) <  6  Then ComboBox1.AddItem c.Value
    Next
   Debug.Print Timer - t
End Sub

    s = "?"
    For i =  1  To  5 
        Range([c1], [c1].End(xlDown)).AutoFilter  1 , s
        s = s & "?"
        If r Is Nothing Then
            Set r = Range([c2], [c1].End(xlDown)).SpecialCells( 12 )
        Else
            Set r = Union(r, Range([c2], [c1].End(xlDown)).SpecialCells( 12 ))
        End If
        Cells.AutoFilter
    Next