When you say something is at six o’clock you should let the person know if you mean a.m. (morning) or p.m. (night). These words are abbreviations for the Latin terms “ante meridiem” and “post meridiem,” which mean before midday and after midday.
“I think I overslept, what time is it now?”
“It’s 12:30.”
“12:30 a.m. or p.m.?”
“12:30 p.m.“