When will Apple ONE become available?

Doesn't matter. What matters is what Apple calls fall. And that can mean anything they want. Patience.

Not yet. Apple announced "coming this fall".

As Terence Devlin said, it's up to Apple.

I'd consider fall as the astronomical autumn: 22 September 2020 – 21 December 2020.

Apple CFO Luca Maestri told Bloomberg that ‌Apple One‌ will launch on Friday, October 30.