From the very first sentence of "The Secret Miracle," it's pretty clear that this story plays with the conflict between an objective, historically-rooted reality, and the subjective experiences that occur within a person's mind. The many different ways that Jaromir experiences time – in dreams, in circular obsessions, in literature, and finally, in a kind of suspended-reality in which the physical universe freezes – are all a little bit different (and a lot hard to understand!). But Borges never says that any one reality is more "real" than any of the others. Instead, he prefers to give us a little taste of a whole bunch of different interpretations so that we'll think about it from all angles. So what do you think? Are you with Borges or is Jaromir just a crazy-pants?
This story is an exercise in subjectivity: the fact that it opens with a dream is a clue that the most important events of "The Secret Miracle" take place within the protagonist's mind.
In his book, Jaromir argues that "time is a fallacy" (4). Jaromir's own personal experiences in prison totally support that idea.