User blog comment:Xilinoc/Ch. 593 - Marching Out the ZOMBIES 4/@comment-29449108-20140820150921/@comment-1268838-20140820231314

I was under the impression that he had done it right during this fight, when he hit Hitsugaya's knee with that weird bomb thing. If that's the case, then Mayuri's statement is more of a taunt than a big mystery - he knows that Hitsugaya cannot possibly know how long ago the drug was administered, since he has repeated this scenario at least ten times already.