Add the chocolate in the last 5 minutes of the boil and you will get more chocolate flavoring. I see no reason to boil it for longer than that, it will only realease flavors and scents the longer you boil.
I have added chocolate this way to a Porter and a Mint Stout. Chocolate came through nicely.
Let me know how it turns out for you John. This was the first beer recipe I ever came up with all on my own (wasn't a clone/change to someone else recipe). It warms the cockles of my heart to see someone else wanting to brew it.
Hoping someone responds quickly. I am racking into the secondary and I am wondering if I over did it with the banana flavors. Should I continue to plan to add bananas to the secondary? How much banana is in the final taste profile?
It had a really nice banana flavor to it when I made it last. Not overly done, but you could taste them. Putting them in the secondary doesn't add much flavor, but intensifies the smell and bumps the ABV a bit.