How to translate a baking recipe for box mixes for cast iron skillets?
I follow the directions on the package, with one modification: when preheating the oven, I preheat the skillet in there as well. 

I add the batter or dough to the warm skillet then bake. I use the baking time on the box as a reference, but monitor by eye toward the end. It usually is done within -5 to +3 minute range as listed on the box.

I've done this with Jiffy corn bread, cake mixes, brownie mixes, etc. Usually very good result. Sometimes the bottom crust is thicker, but the kids liked that. I've never had anything come out as a complete disaster.

Oh.. I also spray the pan with non-stick just before pouring the batter.