Step-by-step explanation:
It depends on the poison. I am personally familiar with strychnine, arsenic, cyanide, ricin and Cloak of Gold D-toxin. Depending on dosage: D-toxin is rapid at 15–20 seconds (symptoms - tingling of fingers and toes); Cyanide is miserable (asphyxia cell by cell) over a period of 3–5 minutes; and ricin kills within 72 hours (great for disassociation for killer, but with symptoms of dying from extreme flu or toxic shock).