alertDialog = new AlertDialog.Builder(this).create();  
alertDialog.setTitle("Alert 3");  
alertDialog.setMessage("00:10");
alertDialog.show();   // 

new CountDownTimer(10000,1000) {
    @Override
    public void onTick(long millisUntilFinished) {
       alertDialog.setMessage("00:"+ (millisUntilFinished/1000));
    }

    @Override
    public void onFinish() {
        info.setVisibility(View.GONE);
    }
}.start();