Dying from carbon monoxide poisoning usually only takes minutes if there's enough carbon monoxide.
Usually within about 15 minutes you can be dead if you have a carbon monoxide leak. It's a silent killer and you should have a carbon monoxide detector installed in your home to wake you up in the event of a carbon monoxide leak.
Make sure to have your furnace inspected yearly as well as any other things in your home that produces carbon monoxide.
Also never run a generator indoors because that too can lead to death from carbon monoxide poisoning.