Interesting. A few months back I watched a youtube video probably about that case in the "real crime" scene. According to their description death of that victim came within "seconds" probably the amount of KCN (CN- ions was huge) Yes the more KCN is consumed at once the higher the chance is to be dead irreversably. The question here is only, how fast is unconsciousness reached and what does the one who CTBs feels during that time. I compare it a bit with full suspension hanging. There are videos from people who performed it and they hardly made any attempts to "rescue" themselves which I would say is the best case that one was definitely unconscious. But there are other videos that clearly show that people tried to "rescue themselves for minutes" and that indicates that those were not unconscious within seconds.