I'd say the best hours for winter steelheading are the daylight hours.

Well, okay, the morning might be best, but there are a couple situations when I've had hot fishing repeatedly all through the day. One is high water, particularly after a long dry spell. The fish will push through all day and can be picked off again and again in the same location. Another situation is rapidly falling levels, but don't we all know that? And a third...well...if you find a honey hole that receives shade late in the afternoon, pound it until the sun goes down.