Clock description: Hour hand between 8 and 9. Minute hand one minute-mark past the 6.

One morning when you leave your house, you witness an automobile accident in your street. You look at your watch when it happens. Later that day you are invited to the police station to give a formal witness statement about the accident. The police officer is trying to establish a detailed timeline of the event. He asks you: "What time did the accident happen?" You remember that it happened at the time shown on the clock as given above.

How would you answer in this situation? (Fill the blank)

"It happened ___."

Actual time shown: 8:31
Answer: "It happened 20h31."

Why did you choose to answer this way?
I worked on the 24 hour time system