23:27 should be no problem, usualy they start the fireworks just when it is dark enough, which can be 10pm ... really depends on the day itself. Expect a heavy crowd cause the japan day has become really famous even for non-japan/anime fans etc. ... it drags millions of people. So count in the time you need to fight truh the mass of people from the Ruhruhfer Promenade to the next subway and from there to the maintrain station etc. ^^; I never did blurb so much before lol...