I suspect longer than 5 minutes - and I would think there is even a possibility that fitness may have a negative correlation (i.e. someone who is less efficient at using their available stocks of oxygen may be able to keep it lasting longer).
I used to be able to hold my breath (granted, after hyperventilating) for at least 4 minutes (when I was a teenager - this was underwater). The main issue is, don't panic, since anything that raises your heart rate will increase your oxygen consumption - so you want to slow everything down as far as possible in order to conserve oxygen. If the victim was suffering from hypothermia, I would imagine they could survive even longer while being asphyxiated.
I would think that it might well be possible (but not inevitable) to survive 7 minutes before becoming unconscious, and then some minutes more before brain death.