A night owl is a person who comes alive after midnight. A natural night owl.
It is partly genuine biology rather than habit, since body clocks differ by hours between people. A night owl in a nine to five job is permanently short of sleep.
1phrasenight owlA person who comes alive after midnight.
“She was a night owl and did her best work after eleven.”
night owl is a person.
Night plus owl, from the bird's habit of hunting after dark.
From night + owl, from the fact that the bird is active at night.
Etymology from Wiktionary, CC BY-SA
Practised in Idioms