I try to roate them around the 10,000 KM mark (62000 miles)

 

For Mud terrains i will be rotating every 3k when i get my oil changed. As for All terrains i did them every 6k or so

 

Every 6k is fine with the mud terrains. If you have a good all terrain tire and spend most of the time on the street you don't really need to rotate them at all unless you want to get the fifth in. I used to drive a lot and on all terrains and mostly highway they were fine for 20k miles when I would then do a balance and rotation together.

The mud terrains wear more unevenly, specially in the jeep. But going every 3k is overkill IMHO, on the other hand you can't over rotate them and it would be a little more pleasant on the ears for those first few hundred miles.

There is no reason whatsoever to not rotate the spare in when it is full sized other than being lazy. Putting a full sized tire on the same axle as a worn down tire (specially when it is 32") is going to cause unnecessary wear on differential, and potentially be unsafe. Don't believe that? Go ask a tire dealer to install one new tire, they won't unless they shave it down to similar diameter. They will put two new tires on the back, that is it.

Rotate the 5th in because otherwise it might as well be a doughnut spare.