How important is the treatment of time in "The Tell-Tale Heart"?
Time is quite meaningful and important to the story. First, the narrator refers to time frequently. He says of the old man who he plans to murder,
. . . every night, about midnight, I turned the latch of his door and opened it—oh so gently! . . . And this I did for seven long nights—every night just at midnight . . . .
Midnight is an important symbol: it is representative of the complete death of day and often is used figuratively to refer to death in general. The fact that the narrator approaches the old man's room to kill him, just at midnight every night, is laden with symbolism then.
In addition to referring to the time, especially the midnight hour, so very often, the narrator also frequently mentions timepieces. In one such reference, he says that, as he opens the old man's door, "A watch's minute hand moves more quickly than did [his]." He compares his own movements to that of a watch. Clocks are often used symbolically to refer to mortality since they keep track of time. We see this symbolism recur when the narrator says that, as he directs the ray of light from his lantern on to the old man's eye, he heard a "low, dull, quick sound, such as a watch makes when enveloped in cotton." He interprets this sound to be the old man's heartbeat, but this cannot be possible; he could not hear another person's heart beating from across the room. Later, he hears this sound again after he has murdered and dismembered the old man, and so we might understand from this that the sound he hears is actually his own heart beating, sounding like a watch, a symbol of mortality.
The connection of these symbols—midnight and the timepieces—can lead us to the interpretation that it is actually his own death that the narrator fears. This is why he's obsessed with killing the old man at midnight, so that he can usurp death's role instead of fearing it. This is why he compares the sound of a human heartbeat to a watch's ticking: he cannot escape his sense of his own mortality and his fear of his own death, though he doesn't seem to realize that it is this fear that compels him to murder.
When the madman narrates his tale, time just drags by, almost coming to a standstill until the instant of the murder. This helps heighten anticipation, suspense and the even the sense of horror. Then as he leaps into action, so the pace of the story line also speeds up until the arrival of the police the next day. Then the whole process of waiting and anticipating and mounting stress repeats itself all over again. Only this time it crescendoes to the revelation of the murder (as the cymbal in an orchestra sounding off) instead of the murder itself.
Poe has been called the master of short stories. He even wrote an essay about it, stressing the importance of working towards a unified effect. His model seems to be inspired from the same "rules" for Greek drama - unity of setting, time and action. As for time, he stressed that the lapse of time in a short story should normally be very short (24 hours or less). Several of his short stories are exceptions, but this is the rule of thumb to go by. Check out the reference below for more information concerning this.