type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    FLastTick: DWORD;
  end;

implementation

procedure TForm1.FormCreate(Sender: TObject);
begin
  // this line is not necessary; the FLastTick will be initialized to 0
  FLastTick := 0;
end;

procedure TForm1.VTFocusChanged(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex);
var
  CurTick: DWORD;
begin
  CurTick := GetTickCount;
  if CurTick - FLastTick > 1000 then
  begin
    FLastTick := CurTick;
    Sender.InvalidateNode(Node);
    PostMessage(Handle, UM_VT_CHANGED, Integer(Sender), Integer(Node));
  end;
end;