Now, 8:30 is “halb neun” in German (literally, “half nine”—presumably because the clock is half of the way between eight and nine, i.e. it’s half-way to nine), but “half-past eight” in (my variety of) English.
Amy seems to have trouble with this distinction, perhaps because they sound so different (with “eight” vs “nine” being the prominent number)—if Stella has promised her that she may stay up until “halb neun” and I tell her that it’s now “half-past eight” and she has to go to bed, she says, no, she’s allowed to stay up until half-past nine.
Makes me glad that my native variety of English doesn’t use the shorter “half eight”, as some people (only in the UK?) do; that’d be even more confusing for her, I’m sure.