How to set interstitial ads to be show for each n seconds ?

ScheduledExecutorService schedul = Executors.newSingleThreadScheduledExecutor();
schedul.scheduleAtFixedRate(new Runnable() {
    @Override    public void run() {
        Log.i("start interstitial","interstitial has been start");
        runOnUiThread(new Runnable() {
            @Override            public void run() {
                if (mInterstitialAd.isLoaded()) {
                    mInterstitialAd.show();
                } else {
                    Log.d("interstitial", "The interstitial wasn't loaded yet.");
                }

                loadInterstitialAd();
            }
        });

    }
},45,90,TimeUnit.SECONDS);