Owls are most often seen and heard during the night, because they are nocturnal. That means they're active at night and sleep during the day.
However, some owls, such as the pygmy owl, are active at twilight. And if you see or hear an owl during the day, it means that you are likely encountering a diurnal (daytime) owl that sleeps at night just like we do—two diurnal owls are the burrowing owl and the short-eared owl.
The Tawny Owl is a widespread and common species throughout much othe UK, where it is normally considered to be a predominantly nocturnal species.
Recently though, I’ve been hearing Tawny Owls calling quite frequently during daylight hours. It often occurs between 10.00 am and 3.00 pm, and often takes place in bright sunshine.
Most probably there is a nest nearby with newly fledged young: owls sometimes call in the day if they feel their young are threatened, and a hunting parent may sometimes call to its partner who is guarding the nest.