How long should an 850 sit after driving before the O2 sensor can be replaced? I have heard they get quite hot and need some time to cool off before they can be worked on. I've got a questionable one and will be making an appointment in advance with my mechanic since I'd need it by 4PM on the day I set aside to take it (they open at 8AM but I'd prefer to get there a little later if possible).

 

Exhausts cool off quickly, probably not long. You can always wear gloves and touch it.