How long does the narrator take to execute his plan in "The Tell-tale Heart"?

It takes the narrator of “The Tell-tale Heart” a total of eight days to carry out his plan, but he actually kills the old man in one night—and gets caught the next morning.

I was never kinder to the old man than during the whole week before I killed him. And every night, about midnight, I turned the latch of his door and opened it—oh so gently! (ch 4)

The narrator takes a very, very long time to stick his head through the door.  It took an hour to get his head through.  On the eighth night the narrator finally acts.  He takes care in opening the door, and the old man sees him and shrieks.  He then throws the bed on top of him.

But, for many minutes, the heart beat on with a muffled sound.  …. At length it ceased. The old man was dead. I removed the bed and examined the corpse. Yes, he was stone, stone dead. (p. 5)

The narrator cuts the old man up and sticks him under the floorboards, and then police arrive because they have heard the old man’s scream.  The narrator lets them in, asks them to look around, and has them sit in the old man’s room above the body.

They talk for a time, but the narrator is getting more and more anxious.  At first he just wanted to prove that he was not guilty, but the imagined sound of the dead man’s heart gets to him and he confesses.

How long does the narrator take to conceal the body in "The Tell-Tale Heart"?

The narrator of “The Tell-Tale Heart” frequently mentions time, particularly when informing the reader of how slowly and cautiously he proceeded. He says that he would open the old man’s door at about midnight but that he moved so slowly that it took him an hour until his head was entirely in the room. On the eighth night, he says, he was more cautious than usual, and a watch’s minute hand moves more quickly than he did. When the old man sat up in bed and called out, he kept quite still and “did not move a muscle” for a whole hour. When he had finally killed the old man, he held his hand on his heart for “many minutes.”

The narrator says that it was four o’clock by the time he had finished concealing the body. Therefore, if we accept his timings as accurate, it must have taken him between one and a little less than two hours to conceal it (starting at midnight, finishing at four, and allowing over two hours for the time spent waiting in the old man’s room, actually killing him, and checking for a heartbeat afterward).

The narrator of “The Tell-Tale Heart,” however, is exceptionally unreliable even by the standards of Poe’s narrators. When he tells us that it took an hour to move his head a few inches, this must surely be hyperbole. The fact is that we cannot reliably determine anything about the story, including how long it took or even whether it happened at all, since the man who continually assures the reader that he is not mad is, at any rate, far from being sufficiently sane for us to trust.