For the sake of ease of imagination, maybe it's good to use a Machian defintion of time, time is the relative configuration of all physical bodies+fields. I also want to be agnostic about the flow of time if possible (e.g. is it fundamental or emergent for entities like us).
I can imagine time doubling or halving as producing no discernable effects because if everything is relative how could one tell?
I can't imagine reversing the rate though. It does not seem enough to say one would just see eveything reverse. At face value, it seems like no matter what, all physicalists would say a signal traveling to the brain is necessary for an experience or sensation, and all signals travelling away can't produce any experience at all. You certaintly wouldn't see a glass unbreaking, photons leaving the eyes would impede that. But you wouldn't even conceive anything at all right, let alone see? Not just a zero value for experience, a NULL value, or maybe better that whole category doesn't exist. Observers simply don't exist with that constitution?
Do physicalists provide any intuition on this?