"It's three o'clock."
Do clocks chime at all, these days? If a non-mil-spec chronometer makes a chime whilst you sleep is anything heard at all? Either way, your prompts in English should not use the archaic "o'clock" form at all if they cannot be used correctly. Reminder: fifteen o'clock does not occur any more than twenty o'clock. These should be changed to use a twelve hour AM/PM time instead.
Klingon has two time-telling systems: military time (wa'maH vagh vatlh rep fifteen hundred hours) and clock-chime time (wejlogh Qoylu'pu' it is heard three times).
This section is teaching clock-chime time. I suppose another section teaches military time. (If not, one should.) Both are valid ways of telling time. There's no reason one should be avoided.
Normally with a prompt like that I would set it to accept answers that referred to 3 am as well as answers that referred to 3 pm. However, the sentence has already been updated to clarify that we are talking about 3 am. It may still take a few days for the update to show up in the actual course.