meaning - What are the nuances of the British expression "gone" used with time, as in "gone 8" or "gone midnight"?

An expression I have run across in British novels is "gone [hour]" like this:

"It was gone midnight, and the house was quiet." The Midnight Witch by Paula Brackston

"It's only just gone eight o'clock, Hugo, and Maria hasn't brought our
tea yet." Caribbean Sunset with a Yellow Parrot by Andrea
Frazer

I suspected from context that this means sometime past that hour, generally where I might say "after eight" or "past midnight", which is confirmed in this (closed) post. I appreciated the detail that it isn't used for planning purposes.

I am still wondering about some of the nuances of usage. This question has resisted my attempts at regular research, with most searches turning up pages of meanings for "gone" or "o'clock" but nothing much useful for the full idiom (except for the above-linked question here). I actually asked a cabbie about this when I was in England for a few days last year, but he wasn't sure. (It's surprisingly difficult to strike up conversations about English usage with random Londoners, at least for me.) I also haven't figured out a good way to express or look for the idiom generally, since there are at least fourteen common formulations (gone one, gone two, gone noon, etc.) and "gone" by itself is obviously not useful. So:

1. Is there a limit on how long after the hour you could use "gone"? (I
   know this is not likely precise, I'm just wondering approximately
   how it would be understood by those who use the idiom.) For example,
   if it's 8:50 could you still say "gone eight"?
   (In comparison, I think I would probably only use "after eight" until 8:29; after
   that I would say "eight-thirty" or "after eight-thirty" or "almost
   
   nine" etc.)

   
   
   

   How much does the addition of "just" narrow down the window?

   
   
   

   Does this depend on hour in question? For example, in the first sentence
   above are we to infer that the time was sometime between midnight
   and 1am (or 12:30 or whatever the appropriate cut-off is), or is it
   less specific, meaning generally late at night?



2. My guess is that this expression comes from something like "midnight
   had come and gone"--does anyone know any more about its origins than
   
   that?


3. Are there any situations besides the hours of the day that this
   usage of gone would be appropriate? For example, "she's gone
   fourteen weeks pregnant" or "my baby is gone eleven weeks old" or "it was gone summer by the time the
   plantings were ready"?

Many thanks for any insight, and my apologies if this question is unduly fine-drawn. Obviously, I've been wondering about this a lot!