Carbon Monoxide can take from 8 hours to even 24 hours to fully leave your body and your breath depending on how much carbon monoxide you've breathed in.
The carbon monoxide leaves your body and breath the same way it entered your body which is through your lungs so you need to breath in fresh air to remove the carbon monoxide from your body.
Within 6 to 8 hours you should have at least half of the carbon monoxide out of your body but it can take a full 16 to 24 hours to clear all the carbon monoxide out of your body.