Show interstitialAd after 30 seconds Audience Network Facebook

I want to use Facebook Audience Network for my Android app, I have integrated interstitialAd in-app and it works fine but it appears as Activity launch. I want to show ad after 30 seconds. this is my code

 interstitialAd = new InterstitialAd(this, "1555910157949688_1556058954601475");

    interstitialAd.setAdListener(new InterstitialAdListener() {
      

        @Override
        public void onAdLoaded(Ad ad) {
            // Interstitial ad is loaded and ready to be displayed
            Log.d(TAG, "Interstitial ad is loaded and ready to be displayed!");
            // Show the ad
            interstitialAd.show();
        }

       
    });

    interstitialAd.loadAd();

and I have tried this to schedule my ad but it did not work.

private void showAdWithDelay() {
   Handler handler = new Handler();
   handler.postDelayed(new Runnable() {
       public void run() {
            // Check if interstitialAd has been loaded successfully
           if(interstitialAd == null || !interstitialAd.isAdLoaded()) {
               return;
           }
            // Check if the ad is already expired or invalidated, and do not show ad if that is the case. You will not get paid to show an invalidated ad.
           if(interstitialAd.isAdInvalidated()) {
               return;
           }
           // Show the ad
            interstitialAd.show(); 
       }
   }, 3000); 
}

I prefer to do this:

      Handler handler = new Handler();
      interstitialAd = new InterstitialAd(this, "XXX");
      interstitialAd.setAdListener(new InterstitialAdListener() {
        @Override
        public void onAdLoaded(Ad ad) {
          handler.postDelayed(new Runnable() {
            @Override
            public void run() {
              interstitialAd.show();
            }
          }, YOUR_TIME);
        }
      });

      interstitialAd.loadAd();

And if you want to be more precise, do it:

      final long lastTime = System.currentTimeMillis();
      Handler handler = new Handler();
      interstitialAd = new InterstitialAd(this, "XXX");
      interstitialAd.setAdListener(new InterstitialAdListener() {
        @Override
        public void onAdLoaded(Ad ad) {
          long now = System.currentTimeMillis();
          long timeWait;
          if (now - lastTime >= YOUR_TIME){
            timeWait = 0;
          }else {
            timeWait = YOUR_TIME-(now-lastTime);
          }
          handler.postDelayed(new Runnable() {
            @Override
            public void run() {
              interstitialAd.show();
            }
          }, timeWait);
        }
      });

      interstitialAd.loadAd();