You don’t really need to theorize? The story gives plenty enough context to figure out exactly how the ability works. GER is just amplifying what’s happening in your mind, similar to what Giorno did to Bucci when they first met but times 1000. Diavolo didn’t erase time, have that time reverted to 0, then end up in some pocket dimension where he dies infinitely. That’s just how his mind is interpreting the beat down by Giorno, because, again, just like how Bucci thought he was ducking & weaving Giorno when they fought, Diavolo is just having an out of body experience but like a lot worse. It happens when Gio beams him through his hand, at which point he then stops moving and his delusions of himself and actions take over