@Override
    public void action(ActionEvent e) {
        attendre(3).start(); //3 est le temps en secondes, tu peux le changer
        JOptionPane.showMessageDialog((Component) e.getSource(), alea);
    }

    private Timer attendre(int seconds) {
        ActionListener fermer = new ActionListener() {

            @Override
            public void action(ActionEvent e) {
                Window[] fenetre = Window.getWindows();
                for (Window fenetre : windows) {
                    if (fenetre instanceof JDialog) {
                        JDialog dialog = (JDialog) window;
                        if (dialog.getContentPane().getComponentCount() == 1
                            && dialog.getContentPane().getComponent(0) instanceof JOptionPane){
                            dialog.dispose();
                        }
                    }
                }

            }

        };
        Timer t = new Timer(seconds * 1000, close);
        t.setRepeats(false);
        return t;
    }