I am by no means an expert, but I've caught a few. Some of them have been at 0 dark thirty, but most have been throughout the day. Give a darkish, cloudy, drizzly day on the Willamette or Columbia, and I think you're fishing effectively from 5:00am to 8:00pm.

I've also caught more than a few on the columbia in the height of summer, middle of a sunny day (while fishing for steelhead. Once on a worm while trolling for walleye.

In smaller rivers, I suspect they would be more sensitive to time of day. In the Columbia, get the lure wet, keep it wet, net the fish. Repeat until satisfied or out of beer.