"Help us! We're in the cellar of Malfoy Manor, help us!"
--Harry Potter, to the shard of mirror (DH23)
Narcissa brings the captives into the drawing room so Draco can positively identify Harry. He does so reluctantly and half-heartedly, but before the Dark Lord is summoned Bellatrix tortures Hermione and Griphook for information about the Sword of Gryffindor. During the torture Harry and Ron are brought to the cellar where they find Mr. Ollivander and Luna have been kept prisoner. Dobby arrives to help everyone to safety. Harry and Ron escape the cellar because of Wormtail’s hesitation which enables them to surprise the people in the drawing room. Harry and Draco wrestle over a handful of wands, Dobby drops a chandelier on the scene, then Harry, Ron, Hermione, Griphook and Dobby disapparate to Shell Cottage, but not before Bellatrix throws her silver dagger.
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 these events 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.
From the Web
"Confused by Potter? Author sets record straight" from Today.com
"On the Elder Wand" from Mugglenet