mostly night, but they learn that food tastes good during the day too! it's easy enough to coax them out, but they don't really get busy with the lights on. Of course there will always be exceptions though....
Most catfishes are usually night active but several familly are also day active, the probably best know familly for day activity is without any doubt Callichthyidae...
Cheers
Yann
I spent twenty minutes or so playing with a 2" gibbiceps the other night. I had my hand in the tank, gently touching it at first, then picking it up. Withing ten minutes it was dancing around my open hand, giving each of my fingertips a good rasp. Very odd experience