Soft science vs a hard science, we can determine anytime a meltdown happens (whenever temperatures are high enough to breach containment, from partial to full) and no amount of PR talk is going to modify hard science.

This is utter pedantry, and I think you know it. I could substitute the "soft science" of 'psychiatry' and the layman term 'crazy' with 'doctor' and 'sick', and the point stands. Hell, we could go blue collar and substitute them with 'Automotive repair technician' and 'running poorly'. You want to call professional preciseness "PR talk," because that suits the narrative of your whatever your agenda is.

Go and ask a doctor what the earliest is that they could tell if a patient was "sick." Don't say with what, just "sick." Be prepared for a blank stare, because what you've asked is such an unscientific, nonspecific question as to be unanswerable without considerable presumption on the part of the doctor you're asking.

Go ask an automotive technician what the earliest point he'd know that a car was running poorly. Guess what, same look. Because you're coming to someone who has a lot of technical knowledge and asking them to succinctly answer a question with hundreds and hundreds of variables.

The reason they don't list "Meltdown" as a thing in technical manuals is that it covers SO many events which are very different from a practical standpoint--that is, whether there is something they can do about it, and what that thing is. If they listed "meltdown" in the manual, or "sick" in medschool or "running poorly" in an automotive trade school, that would make these very technical fields kind of useless. Imagine going to your doctor with strep throat and he diagnoses you with "sick." Well, you get it, but what is that really worth, since there are prognoses to come, treatments, medications. It'd sure be hard for pharmacologists to do their jobs if they're stuck using lay terms. It's not PR talk; it's preciseness borne of YEARS of training to be as accurate as possible, so that you can work with peers who possess an equal level of technical education.

But here comes a layperson, demanding to know when the soonest somebody on the surface might know about a "meltdown."

Okay, what kind of meltdown is this? How is the plant designed? How old is the reactor? How far below ground is it? How are heat and steam vented from it? Is coolant getting to the reactor? Is there radio communication with the surface? Who is this "someone" we're referring to? Is he an employee at the plant? What is his degree of technical understanding? Is "someone" just a given rando chilling out at the Sonic Drive-thru in the nearest town? Is "someone" the director of the IAEA?

These are just some of the hundreds of unspecified variables in the kind of nonspecific, untrained question from the drama. The reason a scientist might be hesitant to just accept the term "meltdown" when answering is because he's also heard lots of different definitions, because it's a lay term.

In conclusion, you're going to dismiss everything I've said here because doggedly promoting your agenda is more important to you than intellectual ingenuousness. But nobody cares because they've already written you off as a wacko and I just wasted ten minutes typing all this into my damn phone.