Exactly. A fact is something that can be objectively confirmed or rejected. Exactly what a specific person likes is a fact, because it can be verified/falsified by simply asking them. An opinion, by contrast is 'Elephants are large.' The reason that's an opinion is because while it seems obviously true, it's subjective. Similarly, grass is purple with pink polka-dots is a fact. It's obviously false, but of course right/wrong has nothing to do with fact/opinion.
_All_ statements are only valid inside the window within which their understandable context stays constant, facts or otherwise.
> "Verifying an opinion X at time T does not entail X at time T+1."
And verifying that my cat weighs 9.5 lbs now does not entail that he will weigh 9.5 lbs tomorrow, but "my cat weighs 9.5 lbs" is not an opinion; it's a statement of fact from measurement/observation and implies "extrapolated from the last specific check done in the usual way" unless explicitly stated otherwise because that's how language works in polite society. "I like green" is the same.
"My cat weighs 9.5 lbs" is only true within a context of a particular moment and location and measurement apparatus and understanding of cat and ownership and 9.5 and lbs.
"1+1=2" is only true within a context of what "1" and "2" and "+" and "=" mean.
> "Opinions can only be seen as facts when modelled as time series data."
Opinions can never be seen as facts, timestamps or otherwise. Only facts about opinions can be seen as facts, not the opinions themselves.
"Green is good" is never a fact regardless of whether you timestamp it. "Green is good right now" is not a fact. "Green was good yesterday" is not a fact. "BugsJustFindMe thinks green is good" is a (false) fact, "BugsJustFindMe said green is good" is a (true) fact, and neither one is an opinion at any time.
> "Verifying an opinion X at time T does not entail X at time T+1."
A constraint binding timeliness specifically to opinions is misplaced and also not extremely relevant in the context of whether something is a statement of opinion or fact.
An opinion is a particular subject's belief [1]. That's literally the definition. "X believes Y at time T", is a fully specified fact and completely follows from the definitions of all terms involved.
None of that has anything to do with whether opinions can ever be considered facts. X believes Y at T is not the same as Y at T, and a statement about an opinion is not the opinion itself. Anyway, we're going in circles now and that's uninteresting to me.