If you're experiencing delays like this, it's not related to the use of an external vs. Marketo-hosted page. It could be that your instance as a whole is backed up, which users on multiple pods have experienced of late (search the Community for details).
The Filled Out Form activity is not in fact logged by Munchkin. Are you seeing that activity in the lead's ActLog? Can you post a link to your actual page so one can check if Munchkin is installed correctly?
Thanks Sanford !
We just got lucky and can track leads now. I think it might be taking that much time because we have a new setup.