O. hummelincki is considered diurnal (day active) but in the home aquarium we see diurnal and crepuscular (early morning, early evening active) animals be anything from what you would expect to anytime of the day or night (nocturnals remain nocturnal and I suspect it has to do with eye sensitivity). My hunch is that human activity and feeding time may alter their natural activity OR we really don't have a good idea of their in situ activity times.