Similarly, when I moved from the UK to Canada, people often didn't understand what I meant when I said it was "half ten", which is the common way of saying ten thirty, at least where I grew up.

Some Americans say ‘a quarter of X’ and even after 30 years I can’t remember if that’s before or after hour X.

I’m a “quarter past” person but I’ve always been confused by “half ten” (which thankfully isn’t used in Australia). But in German, “half ten” means 9:30, which is make more sense to me (probably because I’m used to how German speech often drops words, which is less common in English)

Next, go to Germany or the Netherlands where half ten means 9:30.

I never heard that when I lived in the UK in the 70s, but only in Ireland in the late 90s.

Half ten? So.. 5. Got it.