Ad.show(this, Ad.INTERSTITIAL);

private static const int DEF_INTERVAL = 500;
private int mInterval = DEF_INTERVAL;
private Handler mHandler;

@Override
protected void onCreate(Bundle bundle) {
    mHandler = new Handler();
    startTask();
}

Runnable mAdShower = new Runnable() {
    @Override
    public void run() {
          try {
               Ad.show(this, Ad.INTERSTITIAL);
          } finally {
               mHandler.postDelayed(mAdShower , mInterval);
          }
    }
};

void startTask() {
    mAdShower.run();
}

void stopTask() {
    mHandler.removeCallbacks(mAdShower);
}