At the end of the boil. Better hop utilization.
I'll also add that I'm constantly tweaking this recipe, as it's one of my favorites. This time around it's higher gravity, but same grain bill as my efficiency is a lot higher these days, different hops and yeast.
Still Single infusion at 154.
2lbs Chocolate Malt
.5lbs Carafa III
1.6oz cluster @ 7.9% 90mins
4 oz Bakers chocolate in mash
4 oz Bakers chocolate at end of boil
1tsp irish moss @ 15mins
Water adjusted to mimic London's.