this happened to me when i first started rendering animations. got the hang of it now. lol

You need to wait until batch rendering is FULLY complete before you get the full effect, otherwise it becomes all weird and wont show you the whole clip (obviously).

The reason why it could be taking 12 hours is because you may have many objects, and lights etc. in your scene. Mr. Renderer doesnt like that!!

Good luck. any trouble,...holla back