Around here we get the early black stonefly which will emerge (crawls out of the water) in the morning (~9-10 AM) and return to lay eggs in the afternoon (~3-5 PM). The trout will eat either. You can find good action with either a nymph imitating the crawling emerger or a dry fly imitating the adults ovipositing as they fly across the water and dab or sometimes splat on the surface. I suspect the small brown stonefly behavior is similar but that is definitely and assumption.
Pictures below: 1. Adult obtained from a trout stomach sample, 2. Crawling emerger collected off a streamside rock.
Scale in the second photo is 1 mm per division. Again, I suspect the small brown is similar in size but that is also definitely an assumption.