I was in a game poisoner had necro and I healed the target on night they got poisoned which gave them defense and they got poisoned through the defense and the wiki even says
Your Poison will only take effect the day after you Poison your target. Anyone with Basic or higher defense on the night they're Poisoned will not be Poisoned.
So with powerful defense they still got poisoned on that night (They didnt die they actually got poisoned and died the next night)