D.C.
Good for you for having the conviction to do this.
I don't know much about nursing school, sorry. But, I will say this: Go to your instructors and talk to them. Don't _ask_ if you can have time to pump. Very politely go to them, and tell them that you'll need to pump every 3 hours, and ask them if there is anything they would like you to do in advance to arrange that. Also have a plan in hand to let them know how to will learn anything that you missed during your pumping time. Or, go to them with the schedule and say (again, with courtesy and a smile), that with your new baby you'll need to take pumping breaks, and here is the schedule you'll need to keep (and hand them a piece of paper with the schedule).
I'm a supervisor of a nursing/pumping mom at work. I am fully supportive - I did it myself. But I also can't remember when she needs to take her breaks. I have to much going on to keep that info in my head. It helps me a lot that she gave me a set schedule, written down. I keep it on my desk so that I can remind myself of where she is, in case I'm looking for her because I need to ask her a question.
Added: I would just like to say that the person who said just give formula on those days and forget about trying to nurse has obviously never nursed a child. You can't just not pump for 8-12 hours when you are a nursing mom. It would be incredibly painful, you'd be leaking everywhere, and you would end up with clogged ducts at best, and possibly mastitis. I'm not upset at the person who wrote that, but frustrated with our society about the lack of education surrounding breastfeeding!