Just to offer another opinion, I would say the numbers mentioned so far are pretty conservative. And that's ok, but I definitely take a more aggressive approach to grades in general. I think it's good to sometimes do one or the other, depending on how devastating it would be to lose the player to grades.
I would start a JR out with 0 study hall at least 95% of the time, but I agree a JUCO showing a 2.0 GPA has to get something. I'd probably start about 5 minutes, with a little flexibility either way depending on how much potential he has (i.e. how "scarce" the practice min are). With 5 minutes, I would fully expect the midterms to come back around 2.5 or possibly worse. At that point I would probably bump it up to 10, maybe as much as 15 if it's sub-2.0. Then back to 5 when the new "semester" starts.
The philosophy being, don't waste the minutes until you really need to waste them. We're not running the scholar bowl team here, so any GPA they post over 2.0 with SH minutes is a waste.