From my limited understanding, you have to release the button on the exact frame that the weapon flashes, and then time the DT activation with the contact frames of the attack. There's a couple tutorials and breakdowns of it on Youtube.
LOLOLOLOLOL DmC 15 second boss take down without barely any precise timing as DRI. Just Kablooey, a couple of shots, demon dodge, and devil trigger....which sounds more easy without any kind of practice am I right?
"A rose best blooms near death. You're in full bloom, pal!" ~ Iori Yagami PSN: LatinChris_9990