Owl is not a nocturnal bird by birth. Their sleep schedule is based on the food supply.
Most owl becoming nocturnal because their prey, mice and small animals, came out at night when most danger are asleep. When the food is scarce at night or in this case, food is given in the day, owl could be a diurnal bird. Though this also depends on their diet since there are some picky eater that will not become diurnal even when their favorite prey is hard to come by if they could still find them at night