Like much of this game - and life - there are choices to be made. Better IQ is better, but how much skill development you give up is a question.
It really has to depend on your team. For example, do you have guys with tons of potential - maybe you want to invest more in skills. Or, if you have talented recruits without that much potential to improve - that cuts toward working on IQ. What if you are about to graduate 5 or 6 guys ....that can cut in different ways.
Are you working on a new offense or defense along with the system you run, that matters.....lots of factors.
I spend between 15 and 25 mins on each of offense and defense, usually 20-25. Now, these days I am only in DI with reasonably good teams - I think that IQ is an important way to try to be better than the other guy........but that doesnt mean that you should follow that approach.