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.