In the short story "The Cask of Amontillado" by Edgar Allan Poe, a man named Montresor meets another man named Fortunato outdoors at dusk. He pretends to be happy to see Fortunato, but he has come up with an elaborate plan to lure him into the Montresor family catacombs and bury him alive in revenge because he feels that Fortunato insulted him.

All of the statements in your question are inferred or expressed by Poe in the story. For example, number 1 says that "Montresor and Fortunato are wearing costumes because it is carnival time." This is definitely inferred, because Poe states that they meet "during the supreme madness of the carnival season." The author writes of Fortunato:

The man wore motley. He had on a tight-fitting parti-striped dress, and his head was surmounted by the conical cap and bells.

Montresor is described as wearing a mask of black silk and a roquelaire, a type of knee-length cloak.

The second statement in your question is also inferred in the story, because Montresor does not put on his mask until he has persuaded Fortunato to accompany him to the vaults. Only when Fortunato takes his arm does Montresor slip on the mask and wrap the cloak tightly around himself.

Poe also infers the third statement in the story. Montresor manages to lure Fortunato to the vaults by bringing up his rivalry with Luchresi. He pretends that he does not want to disturb Fortunato and will call Luchresi instead. In reply, Fortunato proudly says, "Luchresi cannot tell Amontillado from Sherry," and then insists that he should go to do the tasting.

The fourth statement is not only inferred but directly stated. While Montresor is building a wall of stones and mortar to imprison Fortunato, he remarks that "It was now midnight." So he and Fortunato remain in the catacombs until midnight and beyond. In fact, Fortunato never leaves.