In the cellar of Malfoy Manor, Wormtail attacked Harry Potter, who exclaimed “You’re going to kill me? You owe me!” Wormtail hesitated at this, and the magical silver hand, sensing the weakness, turned on Wormtail and strangled him:
His own silver fingers were moving inexorably toward his own throat. The silver tool that Voldemort had given his most cowardly servant had turned upon its disarmed and useless owner; Pettigrew was reaping his reward for his hesitation, his moment of pity; he was being strangled before their eyes. (DH23)
Timeline Notes
The real world calendar for 1998 gives us a date of April 12 for Easter. Narcissa states that Draco is at Malfoy Manor for the Easter holidays, so Wormtail's death happened during a two week period including April 12. The books also state that the Trio listens to Potterwatch in March:
But not until March did luck favor Ron at last. Harry was sitting in the tent entrance, on guard duty, staring idly at a clump of grape hyacinths that had forced their way through the chilly ground, when Ron shouted excitedly from inside the tent. “I’ve got it, I’ve got it! Password was ’Albus’! Get in here, Harry.” (DH22)
The only way that the capture by Snatchers in March can happen during two week period including April 12 is if those two weeks begin on March 29. Therefore the capture by Snatchers happened on the evening of March 29, 30, or 31. For this timeline, we'll assign the approximate date of March 30.