How long do the symptoms of carbon monoxide poisoning take to go away?

It depends : It depends on the co level in the blood, and type of treatment available.

Depends on severity: Mild or moderate symptoms can last from less than an hour to many hours, depending on the severity of the carbon monoxide (CO) poisoning, the type of treatment, the victim's other health issues, etc... Studies show the half-life of carboxyhemoglobin (CO bound to hemoglobin) to be about 4 hours (3-5 hr) when breathing regular air, and about 1 hour (30-90 minutes) when breathing 100% oxygen.