It really depends on what you want. We always eat our first night at Chef Mickey's regardless of where we stay, it just gets us in the Disney mood!!! Our last night, we usually like a relaxing night around our resort, so we have time to pack, so for me that would be the perfect night. If you're getting in near dinner time on your first night, might be a good night to hang at the resort. Maybe an early or late dinner at Ohana with the pool thrown in for good measure. I wouldn't do it in the middle of your stay, since it's so short. I'd do it the first or last night, with a leaning towards the last night for a nice relaxing last night at the Poly. Maybe an early PS, and the swimming in the Volcano pool watching Wishes!!