Would it sound awkward if I omit "o'clock" in this context?
Native speaker’s answer
Rebecca
The use of "o'clock" here is to provide context. If you were to hear the word "six" with no context, it would be confusing. You can omit "o'clock" or "am/pm" only if time has been mentioned previously, such as if someone asked you what time it was. On its own, "o'clock" must be used after a number. Ex: I have a meeting at 10 o'clock. Ex: A: What time is it? B: 2. (2PM/2 o'clock are okay also).