Given the amount of heat shimmer that was present initially for the Buff-breasted sandpiper, the stilt sandpipers that kept eluding me, and the fact that the bird is about 5 miles from my house, I've gone back a couple times.
Here it is at midday teed up fairly close to the road.
With the closer, clearer view, the bird turns out to be a fresh juvenile. A moulting adult would have some large fresh winter (and widely brown edged in this species) scapulars contrasting with other worn feathers. This bird's scaps are very even.
In the last light of the evening the bird gets buffier.