You can loop over the active windows creating this method on the class you want to do it:
private Timer createTimerClose(int seconds) {
ActionListener close = new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
Window[] windows = Window.getWindows();
for (Window window : windows) {
if (window 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;
}
And after it you call the metod createTimerClose(secondsyouwanttoclose).start(); before calling your JOptionPane.