For full context:
I think this ということだ expresses "means". "Concerning this...it means (that)". I'm asking for confirmation because my textbook also teaches ということだ as a means to express hearsay or to summarize what the partner in dialogue just said.
My attempt at translation: "Concerning this, it means that when it is past 10 o'clock in the evening, I/we (?) pass time in my/our own room(s)."