At what rate does carbon monoxide posioning affect you?

Usually hours...: ...Because the concentration of co is not that high, but it binds to the hemoglobin on red blood cells very tightly, so does not come off and builds up over time. Example is news reports of person(s) who slept with co leak & died over night--which is why separate co detectors are recommended (+ smoke detector). High concentration environment could build up more quickly, still likely a few hours.