I'd like to know how to explain the rules for use of possessive "s" to describe the quantity of something, as in, "two hours' work" to an English learner.
This answer at english.stackexchange.com, suggests the phrase "...worth of..." is omitted. I don't think anything's necessarily omitted, so it's more precise to say that "worth of" can be added between the "'s" and the noun without changing the meaning.
This sentence is grammatical and idiomatic:
People need between seven and nine hours’ sleep every day.
But these feel somewhere between unnatural and nonsense even though they work fine with "worth of" inserted:
There's 5 million dollars' jewellery behind that glass.
I drove through three thousand kilometres' desert in the last couple days.
I bought a salary's farmland to retire on.
From these, I'm guessing that this possessive "s" structure can only be used naturally with units of time.
Can the possessive "s" with this function reliably be replaced with "worth of"?
Does this structure work only with units of time?
Does this structure work reliably with any noun measured by units of time?
What's the name of this structure's function for easier Googling?