Dave, they bite in low light conditions. the best time to fish for them is an hour before daylight til the sun is up good, or just before twilight til good and dark. You can fish totally at night, but you don't have too.
In my experience, the twilight time seems to work best. But some folks swear by the early morning bite.
I found that May/June is the best time to catch them .. It's when I catch the Most ... However Feb March will have the biggest fish pre spawn opportunity ... there will be a better and more even playing field with more fish being caught after the spawn.
Just down stream from the Dams Dave. 1-10 feet ... They like to spawn in highly oxygenated waters that come from rough rapids.
Highly oxygenate running water keeps eggs clean from sediment. aka rolling