I mean, do they say "I sleep at 9pm" or more like "I sleep at 2100 hrs" even while they are talking informally? 2100 hrs sounds very formal to me, but yeah, I was just wondering if they used 24 hour format for only official and government proceedings and used 12 hour format for casual stuff.
It depends. You might say something like "I've got a meeting from 12 to 14", which is perfectly natural. But also a lot of the time you might just say "I go to bed at 9" because the context makes it obvious that you mean 9 in the evening. Most people don't go to bed in the morning. Unless you do, but then you would probably give context "I'm going to bed at 9 in the morning, because I work nights", for example.
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