Haven't done butternut on the smoker yet. When I do it in the oven, I cut em in half, clean, and put them cut side up for the duration. Take them out when they are soft. Use a small skewer to check. It's been a while, (last fall), but if memory serves, it takes about an hour at 350*. Since yours is smaller, I'm guessing about an hour & 1/2 - 2 hours on the smoker.
Hope this helps, a bit.