Regardless whether it's opt-in or opt-out, the business will need to confirm anything it opted for you by asking. If you don't select the opposing choice in a timely fashion, then the business assumes that it opted correctly in your interest and on your behalf.

> So, I think this is opt-in, until Sept 28.

If the business opted for consent, then you will effectively have the choice for refusal, a.k.a. opt-out.