The chocolates could have been poisoned before Marius left, because...
Estelle Eat Chocolate
Tetrodotoxin Content
Inspection
Summary
At the crime scene, the main character discusses Marius' version of events with Vyn; Vyn points out that the poison used, tetrodotoxin, can take several hours to take effect, so the fact that Estelle was alive when Marius left the banquet may not be helpful to him. Vyn focuses on two facts: that not all the chocolates were poisoned, and that the true culprit already had a syringe on hand with which to poison the chocolates. Estelle's assistant, Jen Mendoza, then arrives for questioning.