Hermes, neuroscience certainly has to do with it, but physics is important, for the reasons explained in the article. I don’t think the Stoics said anything about the infinite divisibility of time, so I don’t think the 200 ms window is a problem for them. By “now” they just mean what we mean in ordinary language, a perfectly intelligible locution.
There is also plenty of evidence in modern cognitive science that we very much can affect our emotional responses by challenging the cognitive assumptions underlying them. Regret is useless if by that term one means dwelling on a past that we can no longer change. If we mean that we should learn from our past experience, the Stoics are definitely on board with that, but I wouldn’t call it regret.
Ironically, it is precisely because emotion and cognition are inseparable — as the Stoics argued — that we can focus on the cognitive part and reduce to nothing the unwanted emotional one.
The Stoics do NOT attempt to reject emotion. That is a common misunderstanding of the philosophy. Rather, they wish to alter our emotional responses — by way of cognition — in a more productive direction. This is definitely possible, as shown by the literature on cognitive behavioral therapy, which is based on the same basic principles.