This answer does cover the duration aspect of your question. It's a rolling 30 day window - a fourth within 30 days is not possible:
3rd ban within the window -> duration: 30 days
As you're automatically in a new window when a 30 day ban has concluded, it rolled over again, and back to the beginning you go.
While this does include 30 day bans that moderators impose, they can in very rare circumstances impose longer periods back-to-back. Possible reasons for this might include:
- A history of rubber-stamping spam posts, or suggested edits that introduce spam
- A long history of failed audits with no demonstrated improvement and no decline in activity (usually accompanied with a "reviews don't seem to be your thing, please stop" message)
To your first question, the late answers queue picks up on any new user that posts an answer to an old question. What we're trying to catch here is:
- Thanks, this helped me!
- Buy discount Gucci socks on my sports blog
- I tried the above, but I still get this error...
- A copy and paste of an existing answer in a bungled attempt to lift new user restrictions
We're not just looking at the answers here, folks also look at the question to see if there might be a reason why an old question continues to attract new answers (is it open-ended? does it need protecting? is it still on-topic by our standards today?)
This used to be accomplished just through the automatic 'churn' of old posts being bumped to the front page as a result of new activity, but our sheer volume these days demands something more comprehensive.
The algorithm itself is pretty simple, one in n items you review is likely to be an audit, but there's a random seed at play too - you could go n(2) iterations before seeing one in some circumstance. It's perfectly fine to fail one or two as long as you are paying attention - audits aren't perfect and can sometimes present you with a very subjective call to make; we take this into account.
Like most things designed to be remarkably simple, it's very difficult to game (well, except for some things that can make an audit obvious, but we're not out to catch folks that are actually, you know, paying attention :))