Because Tweedle described the poison as very fast acting. Within a half-hour, the body can't even hold itself together. Dying probably takes considerably less time than that.

Useful bit of kit actually. Disables instantly, kills quickly, and if the body isn't found for a while then it disintegrates the corpse, which makes autopsy and revival nigh impossible.

Admittedly, if the temporal bomb theory holds, then depending on how quickly time passes within the field, Tarvek may still be savable.