If I had to pick I would say night, however, blues can also be caught just as easily during the day. In my opinion, the best time to catch blues (and other catfish) during the day is the prespawn period from now until about the end of May. This depends on location and water temp., but all cats feed heavily before they spawn which usually happens when the water temps. start getting into the mid 70's, which is usually around the end of May where I live. The bite seems to be better during the night in the summertime after the fish have spawned. Good luck fishin'.
