24h was much more common, though. All the store/place opening times, university/club schedules, bus tables etc. were all in 24 hour time format. Not sure why you’d think 12h is common in Japan, but personally I found the opposite to be true. Although there can be places where it is used instead.
I stand corrected. I was thinking about speaking, where e.g. 午後3時 is more common than saying 15時
I have a Japanese Tandem partner, and at the end of each session we negotiate the date and time for the next one. I don’t know the exact reason, but she always says the time in 24h-format though