三人行，必有我师(焉)

You know, I've actually never known what "half seven" meant, as nobody I know uses that expression, but if I'd had to guess I would have guessed 6:30, because "half seven" sounds like "half of seven" to me -- like, not actually seven, just halfway there -- and I'd have figured if it was after seven, you'd say "half past seven." I mean, if someone tried to schedule "half seven" with me I'd definitely ask what they meant, because I wouldn't be sure! But my first assumption would be that it probably meant 6:30.