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function ShowTrayClock(bValue: Boolean) : Boolean; 
var 
  TrayWnd, TrayNWnd, ClockWnd: HWND; 
begin 
  TrayWnd  := FindWindow('Shell_TrayWnd', nil); 
  TrayNWnd := FindWindowEx(TrayWnd, 0, 'TrayNotifyWnd', nil); 
  ClockWnd := FindWindowEx(TrayNWnd, 0, 'TrayClockWClass', nil); 
  Result := IsWindow(ClockWnd); 
  if Result then 
  begin 
    ShowWindow(ClockWnd, Ord(bValue)); 
    PostMessage(ClockWnd, WM_PAINT, 0, 0); 
  end; 
end; 

// Example to hide they clock: 

procedure TForm1.Button1Click(Sender: TObject); 
begin 
   ShowTrayClock(Boolean(0)); 
end;