Timed Poison

While reading an old book, I came upon a belief that venom and poison could be 'tuned' to only become effective at a desired time after being taken. You could poison someone and nothing happens until its time is reached, then the person dies.

It reminded me of the claims of Dim Mak which is supposed to have been used to kill Bruce Lee. Also called the Death Touch, it involved sudden, rapid pressure applied to a point of the body related to the organ you wish to fail. The Chi circulates through all organs in the body over a 24 hour period, so by 'bruising' the Chi/Blood, when it reached the organ at a specified time after the application of the death touch, it caused failure.

Under the administration of Cardinal Louveis, during the reign of Louis XIV, an Italian apothecary having assisted the lover of the Marchioness of Brinvilliers, who had been sent to the Bastille, to poison the father and brother of the lady, emprisonment immediately became the topic of the day,

and a superstitious opinion was soon generated among the multitude, that druggists and philosophers can compose venoms, which operate, not at the season of administration,

but at definite remote periods; that they can draw drafts upon death payable at one, two or three usances, or even at one, two or three years after acceptance of the order; and that these drafts are unfailingly discharged at their elapse, without a protest or a day of grace.

Not only Quintilian and Theophrastes were ransacked for corroborations of this mischievous credulity; but the annals, or rather the libels, of the modern Italians, were pressed into the service of these calumniators of human nature...

The jealousies of domestic life once inflamed, women thought their innocence, and men their security concerned, in inveighing with bitterness indiscriminate against the buyers of this elixir. Every sudden, every lingering, every conspicuous, every critical diseas was ascribed to the Aqua Tofana. The chief distributors were soon rumoured to be the Italian apothecary Exiii, who administered for secret disorders...