@FredFriendly > "this is English and English norms should be used."
This is actually a very common debate among translators. And as someone who understands a good deal of Japanese, and done my own translations (though I'm not fluent in JPN), I don't think that this should be the case at all. Japanese is an entirely different language from English, and much is lost from keeping strict adherence to ENG. This is why many translators keep honorifics (san, chan, senpai, ect) and other common, untranslatable Japanese phrases. This isn't English, it's Japanese, and it can hurt the story to pretend like they are speaking ENG.
That said, I don't think there'd be a problem with expressing the time as 19:00. However, similarly, there's absolutely nothing wrong with expressing it as 19 either.