How do I limit Firebase Storage downloads to a certain maximum amount per time period per user?

I would like to know how I can limit the download demand in my application, 20 per hour ... I use firebase, no login, the only way I recognize a user and with id de anúncio do google the application only works with internet connection.

Update
If the client makes 10 downloads and returns after 1 hour, the ideal would be to zero the count.

Here is the code I use for download:

 if (Environment.getExternalStorageState().equals(
                    Environment.MEDIA_MOUNTED)) {

                final String STORAGE = mChat = getIntent().getExtras().getString("storage");

                progress = ProgressDialog.show(MinhaActivity.this, "Download...",
                        "Aguarde...", true);
                FirebaseStorage mStorage = FirebaseStorage.getInstance();
                StorageReference storageRef = mStorage.getReferenceFromUrl("MY_DB").child(STORAGE).child(down+".mp3");

                File sdCardDirectory = Environment.getExternalStorageDirectory();
                final File localFile = new File(sdCardDirectory.getPath()+"/Audio",down+".mp3");


                storageRef.getFile(localFile).addOnSuccessListener(new OnSuccessListener<FileDownloadTask.TaskSnapshot>() {
                    @Override
                    public void onSuccess(FileDownloadTask.TaskSnapshot taskSnapshot) {
                        Toast.makeText(Minhactivity.this,"Salvo em "+localFile.getAbsolutePath(),Toast.LENGTH_LONG).show();
                        progress.dismiss();

                    }
                }).addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception exception) {
                    }
                });


            }else{
                Toast.makeText(MinhaActivity.this,"Você está sem Cartão de memória",Toast.LENGTH_LONG).show();
            }

        }
    });

Thank you for the attention of everyone involved right now!