The following is an item in the first core 100 deck in absolute beginner. As you can see, the Korean word 정각 does not appear in the example sentence. The word 시에 is in the sentence and does mean "o'clock". I suspect that 정각 does not mean "o'clock".
Could you please clarify:
정각
(noun)
jeonggak
o'clock
아홉 시에 역에서 만나요.
Ahop sie yeogeseo mannayo.
Let's meet at the station at 9 o'clock.