[hitman797]

    Form1: TForm;
    Viewport3D1: TViewport3D;
    Layer3D1: TLayer3D;
    FloatAnimation1: TFloatAnimation;
    Layer3D2: TLayer3D;
    FloatAnimation2: TFloatAnimation;

      object FloatAnimation1: TFloatAnimation
        Enabled = True
        Duration = 1
        Loop = True
        PropertyName = 'RotationAngle.X'
        StartValue = 0
        StopValue = 180
        OnProcess = FloatAnimation1Process
      end
      object FloatAnimation2: TFloatAnimation
        Enabled = True
        Duration = 1
        Loop = True
        PropertyName = 'RotationAngle.X'
        StartValue = 180
        StopValue = 360
        OnProcess = FloatAnimation2Process
      end

procedure TForm3.FloatAnimation1Process(Sender: TObject);
begin
  Layer3D2.BringToFront;
end;

procedure TForm3.FloatAnimation2Process(Sender: TObject);
begin
  Layer3D1.BringToFront;
end;