It is a widely held position among cosmologists, especially those working on models of what existed prior to the Big Bang.
Time is a convention that we use to make sense of change in the universe. But it doesn’t really exist. Matter exists. Energy exists.
Time does not.
Hmmm, well change seems to imply a ratio whose denominator is in terms of time. Perhaps they are using a number of event states as such a denominator and think of it more discreetly?
Perhaps all things if we would like could be abstracted in one way or another and thought of to not really exist, for some special meaning of existence that is useful to some model or another. For example, I believe some world views hold that matter and energy don't really exist.
"Existence" as a technical word causes more confusion than it helps I think. Its usefulness was eroded by too many philosophers putting too many meanings to it. So I favor using it in the most general non-technical way.
To the fictional characters of a book, the author does not exist (unless the author chose to represent his own person in the story). However the author is more real than the characters in the book.
But under the model you seemed to be describing, the author himself is not real. What is real is the state of the matter in the author at the thinnest possible slice of "time" (whatever that is), and the state of the particles close to the author, that might not be considered the author exactly...and perhaps the rest of the universe at that moment I suppose.
In the mind of the author would be a thought of the characters, so perhaps they are real in that way...but thoughts require a much longer chain of tiny causal steps then the thin tiny slice of now that is the only state that currently exists. Since the future and past don't really exist, well I can't see how thoughts exist. Or the mind of the author for that matter. Certainly the particular arrangement of some particles of matter and some energy that do not constitute a single thought do not constitute a mind.
Seems this view implies that minds only exist in our minds...which don't exist anyway...so we should just stop it!