If it was agreed they'd arrive between 9 and 9.30, I'd expect them to be within that time slot. I'd aim for 9.15 if I were the one due to arrive.
I'm old enough and grumpy enough now to just go out/not answer the door if people can't manage to arrive within a generous time frame. Especially if they've previously managed to ever get to work/the airport/a concert on time. I don't find it charming or funny when people persistently indicate that my time is less important than theirs.
The only exception would be a friend or relative that was usually prompt. If they were late I'd be concerned enough to hang on.