is there a limit on the minutes you would put into offense/defense practice time, above which you stop seeing more improvement in IQ?  I.e. if I practice 25 minutes on both Off/Def, I would think my guys get to an acceptable IQ faster.  But what if I practice 30, 40, 50 minutes on Off or Def?  Would I see guys with their IQ taking off in just a few days or are there diminishing returns?

There are diminishing returns above, I dunno, 20-25 minutes each.  Don't think the extra improvement isn't there - you'll get more improvement for 40 min than you would for 35 - but I think that few people would argue that anything above 30 is cost-effective, and unless you're recruiting mostly high-rating, low-potential guys, anything above 27 is likely too much.

Anything above 25 is wasted. Forget the exact % but there was a thread by trentz or another developer a while back.

I think its a mistake to say that anything above 25 is wasted - rather, above 20 or 25 each minute is less productive - dont know the % but its like each minute over 25 is worth say 0.8 mins - and still less with each added minute

that doesnt mean that it is worthless to go that high or higher - depends on whether your guys skilz are mazxed

Yes as you go higher the rate diminishes. Anything above 25 is minuscule. When hoops dynasty first started, could put 35 minutes into IQ and see dramatic results. Those days are long long gone.