7 frames, not even 0.25 seconds. If the lofty investment seems worth it to you, go ahead.
For the test, I rested at the bonfire and levelled my DEX to 20 and fired a round of Dark Bead. I then levelled up my DEX to 45 and fired another round of Dark Bead. For this reason I can measure the time difference in frames when Dark Bead collides with the steps opposite me.
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Dark Bead is a sorcery in Dark Souls. It can only be found in the Artorias of the Abyss...