This is the 15126th most frequent Korean word.
밤늦게까지
"Until late at night."
밤늦게까지 in this sentence means 'until late at night', indicating the time span the action (reading books) continued.
나는 밤늦게까지 책을 읽었어요.
I read books until late at night.
밤늦게까지 here represents the extent of time the conversation took place, emphasizing it continued into the late hours of night.
우리는 밤늦게까지 이야기를 나눴어요.
We talked until late at night.
밤늦게까지 in this context shows the dedication or effort of students working on their studies lasting late into the night.