In Japan (where they use a 24 hour clock), opening hours for stores/restaurants, or broadcast times for TV shows will often be written as something like "27:00", which would mean 3 AM (24+3).
Although I've also seen a "Track 0" at a train station.
I really really love that here in Germany, places will refer to e.g. "Friday 24:00" to mean 00:00 on Saturday.
The phrase "Friday at midnight" actually means six hours after 6PM on Thursday, of course, so using 24:00 versus 00:00 to disambiguate which day is meant is wonderful.
One way to avoid any confusion when timetabling things is to always schedule stuff for 23:59 or 00:01 -- then it's unambiguously inside one of the days.
Although I've also seen a "Track 0" at a train station.