Java/android how to start an AsyncTask after 3 seconds of delay?

You can use Handler for that. Use postDelayed(Runnable, long) for that.

Handler#postDelayed(Runnable, Long)

Using handlers as suggested in the other answers, the actual code is:

new Handler().postDelayed(new Runnable() {
    @Override
    public void run() {
        new MyAsyncTask().execute();
    }
}, 3000);