fetch.java

firebaseRemoteConfig.fetch(cacheExpiration)
                .addOnCompleteListener(new OnCompleteListener<Void>() {
                    @Override
                    public void onComplete(@NonNull Task<Void> task) {
                        if (task.isSuccessful()) {
                            mFirebaseRemoteConfig.activateFetched();
                            // We got our config, let's do something with it!
                        } else {
                            // Looks like there was a problem getting the config...
                        }
                    }
                });

What is "cacheExpiration" in firebaseRemoteConfig.fetch(cacheExpiration)