My recipe is here:
https://www.homebrewtalk.com/f76/moon-hill-pumpkin-ale-260064/
I added ~30 ounces (2 small cans) to the mash, ~15 ounces to the boil at 60 minutes, and ~8 ounces to the boil at 30mins.
I would have put the full can (15 instead of 8 ounces) at 30 mins, but I ran out. Also, I remember reading someone (I think it was Revvy) say that they added their pumpkin to the boil at 10 mins.
Also worth noting, the first 3 cans of pumpkin I added were caramelized. The last 8 ounces was direct from the can. I kind of wanted a bit of that vegetable "pumpkiny" flavor and color near the end (another reason I was considering a "secondary" addition if there are any fresh pumpkins available at that time).
Although, I did strain out a lot of the pumpkin through a grain bag when I poured into my fermentor, which may have been counterproductive if the pumpkin being in the fermenting wort does add flavor (not sure if it does much or not), but I wanted to avoid a secondary.