It's all conjecture but with the info we have we can make an educated guess to narrow it to ~4 weeks. They could do another announced delay to 2021, but that seems unlikely. The delay that was done they were very transparent about being for "polish" and stated it would still be released in 2020, when they didn't have to open themselves to that date obligation. It would have been easier to just say it's delayed and will be out when ready. But they didn't do that. So there would really need to be a massive significant bug or slew of bugs to cause that. The 9.0 launch has been a little shaky, but nothing I don't think that would cause them to announce a 2nd delay. They'll be very leery about that knowing a 2nd delay wouldn't be received well by customers at all. They are really past the dev point with Shadowlands of major changes that would take a lot of time, and that's not the type of changes they said they'd be doing during this extra polish time.
I also don't think they would have accepted the PR/customer hit of the first delay for just an extra week or two from the original Shadowlands release date. My guess is that Blizzard decided that if they are going to lose some sales to refunds because of the delay that it should be at least a month. That would be about a 1 month window sometime between ~ November 24th and Christmas to cash in on holiday sales.
Beyond that within that window is just throwing darts. But it really should be somewhere in that range. They could also easily do a release on a day other that Tuesday since the base 9.0 patch is already applied, and they gave that as one of the benefits of this launch approach vs. the old all at once update patch expansion launches. It's just a flip of a switch for them now to open Shadowlands. So they can work around individual days that might not be a good fit like the wow anniversary.