yeah it is! Here in Denmark "kl." it is used all the time when talking about time.
Now that I've lived in Denmark for four months, I'll clarify based on what I have observed. Yes, they do use 24-hour time on clocks, microwaves, computers, and so on, but in day to day speech, they use 12 hour. When the 12-hour time is ambiguous, they can add 'i morgen', or 'i aften' to the end to be clear they mean in the morning, or in the evening. In this case, the answer would become "Vi spiser klokken seks [i aften]."