TSN - occasionally throughout the day and then it's game time once the tank lights go out ( stage turning out the display lights and then turning the lights in the room off). I presume at some points during the night he goes back to hanging out, but he gets excited as soon as the room light turns on in the morning.
S. eupterus - Anytime the other fish in the tank get excited to feed they'll come out from hiding. Sometimes they meander during the day though. Once the lights are out they'll take another spin around, but they don't stay out for long.
S. decorus - After nearly all of the food in the tank has ben devoured by other species they'll try to find some. Otherwise they don't come out until after dark.
My plecos - on and off around the clock!