Yes, as the others said, fit it in wherever you can, making the most of lunch hours, perhaps walking to and from the hospital for home, this would be great stress relief after a long day. Also, I know doctors and the like frown on "weekend warriors" because of a tendency to over do and get injured, I have to tell you that this is a routine that works for me! If you have any two days off per week, at least make those the days in which you do it all: a long or intense cardio workout and then work half the body with weights each day, lower on one, upper on the other. This, combined with walks, the odd squats session with lots of low end pulses or tricep dips off a chair in between patients, and runing up the stairs rather than using the elevators, can get you through.
Your goal right now is not to start any new exercise program, not to set yourself a new exercise challenge, but to dedicate yourself to your nursing program and keep your mind and body ticking along while you do.
We all have years of this in our lives. For you it is nursing school, for me it was grad school with small children. Absolutely no time to work out there, so I didn't! Guess what? I am still in good shape now and you can get it all back and go further AFTER your nursing degree is in the bag.
They say there there are things you should never do within 3 months of having a baby: don't move house (my mother and I both did that, she while in labour!), don't start a new job (my husband did that the week after we moved to a new state with our 1 week old second child), etc. This new situation is the same for you: manage your stress levels by being sensible and realizing that you cannot do it all, but you can do all of one (nursing degree) and some of another, just for now. This period will not last forever.
Good luck!
Clare