You are exactly right about Plato - he separates being and time. Plato does this because he sees philosophy as the striving of the psyche towards eternal things, and in order to achieve its goal, it must exclude everything about itself and its world which is finite and changeable. This opens the space for Aristotle's criticism, that such a realm of eternally unchanging forms could not be the reality of the temporal world, because it would have no way to produce change.
But I would have to disagree with the notion that Newton and Einstein argue for the unreality of time. For Newton there is something he calls absolute time, which flows at the same rate regardless of what objects inhabit it or who perceives it. To me this seems like an argument not only for the reality of time, but for its absolute reality. Einstein criticizes this notion, drawing in part on the results of the Michelson-Morley experiment. In order for time to be absolute, the speed of light would have to be relative, but the Michelson-Morley experiment disproved this, and Einstein shows with a thought experiment that their results imply the relativity of time.
Saying time is relative is much different from claiming it is unreal. If you are interested in pursuing this question, I would recommend reading Heidegger's short lecture "Time and Being" and the first chapter of Derrida's "Given Time: I. Counterfeit Money". Rather than simply saying time is unreal, these thinkers point out that it is inaccessible yet absolutely necessary as a foundation of experience. All we can experience are temporal things, yet time is nothing temporal. It does not come to be and pass away, and never presents itself as an object in our world. In this regard it is like being, which never presents itself as a being. Despite being nowhere accessible to experience, the entirety of our experience and thought is only intelligible on the basis of time. All of experience is temporal, and it is just as paradoxical to claim that it takes place without any time, as it is to claim that time, something entirely inaccessible to experience, is the ground of that experience. In this it is like God or death, something which is only possible as impossible.
I'm a bit confused by your last statement. Are you saying that you recognize a contemporary trend towards atemporal physics and mathematics?