Efficiently hiding / unhiding many (+500) rows in Excel VBA

Sub Hideall_butlast_10()
    Dim ws As Worksheet

    For Each ws In ActiveWorkbook.Worksheets
        ws.Visible = xlSheetVisible
    Next ws

    Const lowerBound As Integer = 5
    Const upperBound As Integer = 10

    Dim i, x
    i = Worksheets.Count
    If (i > lowerBound + upperBound) Then
        For x = lowerBound + 1 To (i - upperBound)
            Sheets(x).Visible = xlSheetHidden
        Next x
    End If
End Sub 

Sheets("Prop. Pres. Notes 206-261").Visible = LCase(Sheets(1).Range("G39").Value2) = "yes"

Private Sub check_hidden_area()
  If Rows("1:17").EntireRow.Hidden = True Then
    Range("B18") = True
  Else
    Range("B18") = False
  End If 
End Sub

Private Sub check_hidden_area()
Range("B18") = False
  For i = 1 To 17
     If Rows(i).EntireRow.Hidden = True Then
       Range("B18") = True
       Exit For
     End If
  Next i
End Sub

Private Sub Worksheet_Change (ByVal Target as Range)
   '...
   Call check_hidden_area
End Sub

Private Sub CommandButton1_Click 
   Call check_hidden_area
End Sub