Yes. In October, even with an ADR, I'm often waiting past the reserved time. But, easy way to check - see if there's an ADR available for your date in September
You'll likely always need an ADR, but if you are flexible on the date and time you go its pretty easy to score a last minute reservation. We've only ever made a morning of ADR and haven't had an issue.
Definitely get an ADR. It depends how flexible you are and how long you'd be willing to wait without one but personally I'd make an adr to avoid disappointment.