keep late hours
To tend to stay up late at night. A: "Don't call her right now, it's after midnight." B: "No, it's fine, she keeps late hours."
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.
keep late hours
Stay awake until late at night. For example, Never call Ethel before noon; she keeps late hours and sleeps all morning.
keep late (or regular) hours
do the same thing, typically getting up and going to bed, late (or at the same time) every day.