english
1
general::
Stay awake until late at night. For example, Never call Ethel before noon; she keeps late hours and sleeps all morning.
American Heritage Idioms
2
general::
Phrase(s): keep late hours to stay up or stay out until very late at night. • I’m always tired because I keep late hours. • If I didn’t keep late hours, I wouldn’t sleep so late in the morning.
McGrawhill's American Idioms And Phrasal Verbs