To imply as you do below, "it did not happen" is to say that to establish the covenant the blood must be offered up that very minute. Christ said of the Cup, "this IS my Blood". Since the same God breathed the cosmos into existance out of nothing I can't see the difficulty of the wine becoming His Blood as He commanded.
The covenant was established the evening of the Last Supper as the Eucharist. I think we can trust Christ for a few hours before actually sealing the covenant.
At the Last Supper, in absolute terms, Christ said, , the chalice of wine is the New Covenant. [Cf. Matthew 26:28; Luke 22:20]. His Blood is the Covenant.
And, before the testator's death is He not allowed to grace those who would be intended recipients of his legacy? And as I've said before, wills are often made decades before the demise of the testator. Of course there are no legal rights to the legacy until death, and in Christ's case, on that day the entire universe was remade.
JoeT