My pullets definitely poop the most at night, so that would be under the roosts. I change the bedding under the roosts every day (we're rearranging the whole thing soon anyway). They free range during the day, so they also spread their poop all over the place during the day, but that's okay, because it gets washed away by the rain and is spread out. (except when it's on the deck or walkway... yuck)
But my older hens usually waited until they were let out of the coop in the morning and then did big poops on their way up the path. I hope the pullets eventually do the same thing. Don't they kind of instinctively want to keep their nesting areas clean? I think I heard that somewhere, just like a broody hen will only go once a day or two when off the nest.