I would expect them to arrive at any point between 9:00 and 9:30. I think half an hour is a pretty generous window so (catastrophes aside) turning up much later than 9:30 would be rude. However, I'm autistic, a stickler for timekeeping, and would rather turn up early and sit in my car for twenty minutes than be two minutes late.
If driving, I would give a specific time rather than a window. If taking public transport, I'd say "the train gets in to your local station at 9:12, so I should be at your house by 9:20", then I'd text to let them know if the train was late.