The problem is that you see the RtZ working and not working in a black and white way, it's not that if it works then the whole stuff that happened to Diavolo needs to happen and if the RtZ doesn't work then nothing happens.
Or, maybe, just maybe, it's because it quite literally doesn't function like you think it does Efi, this isn't open to interpretation, debate, or anything of the sort and I'm not about to argue this shit with you. It is black and white, because we know how it functions, we know what it does, we know how it behaves, we know the effects it induces upon activation, so forth and so on, we *******
know how this shit works Efi. What you're saying isn't true, it's factually and demonstrably false, your argument is based upon complete conjecture that relies on RTZ basically not working like we know it to.
it's not that if it works then the whole stuff that happened to Diavolo needs to happen and if the RtZ doesn't work then nothing happens.
You're essentially unironically saying "RTZ doesnt NEED to happen the way we see it function, it could function in a way that's never seen before", sorry Efi, but no, that's not an argument, that's you making shit up to fit a nonexistent argument. Worst part is, even if we take how RTZ is shown to work in EOH, even in gameplay itself, your argument still doesn't hold any weight because it demonstrably doesn't function in such a way where your conclusion and hypothesis is a possibility.
And fyi, if we take the other times we see RTZ used bar the Diavolo scene, it's even worse for your argument because every other time minus that instance is shown to instantaneous, from Point A to Point B with zero delay or time between them, as in, thing happening, RTZ effects it, instantly back at square 1.
The RtZ started to work, Giorno could feel that, but it could not keep on doing what it does because it got nulled.
That's not actually said. What's said is that Gio tried to use RTZ and was sure it activated but..., and that's it, he never clarified what the "but..." was, he isn't actually saying what you think he's saying, he could very well be saying "I tried to use RTZ, but it didn't come out or take effect" instead of "I used RTZ, and it started working but then suddenly stopped even though absolutely nothing indicates it began in the first place and isn't even consistent with how the ability is portrayed in the game itself", like **** we don't even hear the RTZ sfx, something tells me it never got going in the first place, it's never stated that it
started to work but suddenly stopped, it may seem like semantics and grammatical nitpicking, but it's actually crucial and I'm gonna have to disagree with you here.
It doesn't matter how the ability works, especially when you remain aware while it happens like Diavolo,
You no shit just said "it doesn't matter how it works", yes it does Efi, you can't just ignore how shit works because you don't like it. Diavolo remained aware for reasons unrelated to what's happening here. Do I need to point out times in both canons where RTZ makes it so the opposing force isn't cognizant?
imagine if while GER was telling him "What you experience now blah blah.." Diavolo just so happen to have and use Power Null to revert everything because his ability to do so>the RtZ.
Diavolo wouldn't be able to do so, because he wouldn't be able to take action

Diavolo no shit has a functional power null in regards to time skip, multiple guides claim that abilities and the like are rendered unusable while time is deleted, RTZ said lol **** you anyway. And if Diavolo just so happened to have a power null that could effect RTZ, he'd have to have used before, or after he was effected, not in the midst of being effected like you're claiming, because that isn't how RTZ works Efi.
Heaven DIO could have done the same right after GER used its RtZ. Or, RtZ started before Heaven DIO's actions got reverted and then he nulled it, because he had the power to do so.
Except he couldn't have, and you realize that "RTZ started but DIO wasn't reverted" is a paradoxical statement, if that was the case, well, RTZ didn't start then. Dio explicitly needs contact at that point, if RTZ so much as started, even slightly, even in the way you
think it functions, DIO wouldn't of been able to do anything because it would've been to late.
This is without getting into how RTZ is portrayed in game either, or how it'd interact with the rest of the squad theyre there given you're going with the Diavolo scene instance of the ability, which I hope I don't have to explain why that isn't exactly possible.
I'm going to as blatant as I possibly can be Efi, this argument ain't gonna cut it, it's not gonna fly, instead of picking this hill to die on, you could just as easily argue something like "Dio powernulled GER right before he used it, and so nothing happened", there's a throwaway line here and there that could point to that, instead of trying to argue against the media itself and against how the shit works in general.