Common ways to tell the time

Question

I'm a non-native speaker. In school, I was taught that the proper way of telling times in English is X o' clock.

In NAE, would it be common to omit o' clock and just say something like:

It's eleven

in an informal context? Are there other commonly used ways to tell the time?

Answer 1

You can omit all kinds of things.

3:00 is three

3:15 is three fifteen

2:45 is quarter of if the context is "Is it 3?" "No, it's quarter of."

3:30 is half past three or half past in context, but never half to/of four

3:05 is five after three or five after in context

2:55 is five of three or five of in context, or two fifty five

3:01 is three oh one

And, as a general but often violated convention:

1. am and pm aren't used in any context when there's a "normal" assumption Examples: "My flight leave at 3" (normal), or "My flight leaves at 3am" (exception, or emphasis)
2. am is often in the morning and pm is often in the afternoon or evening. Examples: "My flight is at 3 in the afternoon", or "My flight is at three in the morning".
3. 3:00 EST/EDT is three eastern, and the distinction between standard and daylight time is so bungled that people often trip over it.
4. As noted above, of can be replaced with till and to throughout.