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.
For me, it depends. 1700 Hours is definitely weird and military in my experience. But 17:00 isn’t. The difference is how you write and say it. The first reads as 17 hundred hours, while the other is 17 o’clock.