Unlike mayflies, adult caddis are not especially vulnerable to trout when they first hatch. However, they are long-lived (compared to mayflies), and often fall or are blown onto the river. So adult imitations work well any time of year caddis are hatching.
The Elk Hair Caddis is the standard caddis imitation in the West. It has caught countless trout. The fly floats well in rough water, but will works reasonably well in slower water