How to change the duration of app-open ad?

I am using Flutter, and trying to build an app using app open ad(by google admob) and Future Builder. Because future builder takes long, I want to keep the ad displayed for longer than 5 seconds, or close the ad after future builder gets data. I have already implemented both admob, and future builder.

The relationship between openApp ad and FutureBuilder

Could you teach me how to change the duration to show ad?

If you want more information to answer this, please let me know. Thanks!

code:

    AppOpenAd? openAd;
Future<void> loadInitialAd()async{
  await AppOpenAd.load(
    adUnitId: AdHelper.startAppAdUnitId,
    request: const AdRequest(),
    adLoadCallback: AppOpenAdLoadCallback(
      onAdLoaded: (ad){
        print("Ad is loaded");
        openAd = ad;
        openAd!.show();
      },
      onAdFailedToLoad: (error){
        print("ad failed to load ${error}");
      }
    ), orientation: AppOpenAd.orientationPortrait
  );
}

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await MobileAds.instance.initialize();
  await Firebase.initializeApp(
    options: DefaultFirebaseOptions.currentPlatform,
  );

  runApp(MyApp());
}

    class MyApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return 
        return MaterialApp(
            home:MyHomePage());          
    );
  }
}
class MyHomePage extends StatefulWidget {
  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

}
@override
  Widget build(BuildContext context) {
    return Scaffold(
       
        body: FutureBuilder<List<MonumentModel>>(
          future: MonumentModel.fetchMonument(),
          builder: (context, snapshot) {

return 
snapshot.hasData ? Container(child: Widget(snapshot!.data))
                  : SizedBox(child: Center(child: CircularProgressIndicator())),

Without seeing the code it is difficult to help you, but did you check the documentation? Reading the docs, it seems that the ad is not automatically dismissed, which tells me that most likely your ad is dismissed by something else. Probably a navigation event that is used to show your loading screen.

Check the FullScreenContentCallback declaration to see how the ad should be shown and dismissed.