I've spent a lot of time recently with hospice workers. I've learned that they're often asked by their patients, "How much time do I have left?"
While sometimes loathe to offer an answer, hospice staff can predict the timing of the end pretty accurately.
They do so by measuring by the changes they see. Or, more accurately, the pace of change in those changes.
Could a patient pick a book up off the floor in June, but not in July? If not, then their remaining time is likely to be measured in months.
Could they raise themselves out of a chair last week but not today? If not, then it may be only weeks until the end.
Are they losing function every day? Then death is likely just days away.
And so on, right through hours, minutes and seconds.