Learn English – “Not until” and “by”

It’s too late to go shopping. The shops are open only until 5:30. They will be closed by now.

Yes, closed here is employed as an adjective. You are correct in understanding it to designate a state rather than an event.

And it is true that the expression by TIME is used with events rather than states—as your source says, it says that something ‘happens’ (an event) rather than ‘continues’ (a state).

HOWEVER: The expression by TIME does not compel you to employ an ‘eventive’ predicate or forbid you to use a ‘stative’ predicate. In fact, the compulsion works in the opposite direction: when you use by TIME, you compel your hearer to understand the predicate in an eventive sense. With by TIME the hearer interprets a stative predicate as the result of a change of state: something happened before TIME to bring about the state you describe.

Here are examples of by TIME with three stative verbs, know, own, be:

By April he knew that the operation was a failure. ... implies that he did not know this earlier, but at some time before April he learned that the operation was a failure

By 1973 he owned 26 newspapers. ... implies that he did not own so many newspapers earlier, but at some time before 1973 he acquired 26 newspapers

By next week you will be in Toronto. ... implies that you are not in Toronto now, but at some time before next week you will go to Toronto

In the same way, The shops will be closed by now implies that earlier the shops were open, but at some time before now the shops were closed. Since it is explicitly stated that the shops are open until 5:30, we understand that this sentence must have been uttered at some time after 5:30.

The word will may have caused you some confusion. This will does not designate some time in the future; it expresses a certain inference in the present. (Linguists call this ‘epistemic’ will.) Your last sentence may be paraphrased

It is certain that they are closed by now.

The most basic answer to your question is that when and how they can be used all comes down to their definitions. The words "of" and "on" have quite a few variations and so there is no single right way to use them, but several.

• "As to" almost always points to a decision that needs to be made, is going to be made, or can be made. It seems to always be followed by an adverb, but I am not sure whether or not that is the rule.

  1. I am unsure as to how we will go about this. (how to go about this is what must be decided)
  2. As to whether or not you won, I could not say. (The winner has not been decided)

• "On" usually indicates a detailed or direct relation between the subject and its modifying prepositional phrase. Think of it like an object sitting on a table - there is direct contact.

  1. He gave a speech on the ramifications of not wearing protective gear while cycling. (The ramifications were the main topic of the speech he gave.)
  2. She was working on a solution for the global climate crisis. (The global climate crisis was the main subject of her work.)

• "Of" often lends itself to less knowledge or detail on a subject on the surface, though that is not always the case.

  1. I have heard of him before. (I have at least a general awareness of him, but don't necessarily know much more detail.)
  2. Of all the cars, twenty were red. (There were twenty red cars, but specifically which ones were is left uncertain.)

• "About" simply signifies a relation or subject. It can indicate great detail or a general association. Often times "of" or "on" can be used in place of "about."

  1. He knew many things about life and love. (He knew a good number of things about life and love. It's very general. Both of and on can be used here.)
  2. Her story was about the joys of sailing. (The subject of her story was the joys of sailing. Both on and of can be used here, though I feel on would work better.)