This poem is set in a kind of Twilight Zone, with its own laws of reality and no identifiable landmarks of any kind. Almost no concrete objects are mentioned, except for "tears," "sighs," and a faint suggestion of candles. In fact, if we were to film a Twilight Zone episode set to "The Computation," it would be set in a dark room with a single candle burning and clocks with their hands wildly spinning in the background.
The most obvious feature of the setting, then, is the increasingly rapid passage of time. The poem turns the speaker's internal sense of time, which drags out because of his separation from his lover, into a real, external time. By the end of the poem, we're not sure where we are, and neither does the speaker. Will he live, or die? Does he still inhabit the earth, or has he passed on to another realm? There's not much in the way of clues to help answer these questions, so you have to go with your gut on this one.