I won't say I get 8 hours because I'm a chronic insomniac, but I get all the sleep I want to. Here's a key: if you have to choose between studying and sleep, or anything else and sleep, always pick sleep. Seriously. It does you no good to cram for a test and be half awake the next morning and unable to reason through the questions. A big part of nursing school
is getting you to think critically, which is what is going to make you a good nurse (and will also get you to pass boards!). You just cannot think critically when you're so tired from studying that you fall asleep in class, and just knowing the facts you crammed down your throat the night before will not help you get the questions right. Your awake brain will.
Also, do you learn better when you're sleeping or when you're awake?
If you're not fully awake and engaged in class, you're probably going to have to work harder to learn the material than you otherwise would, which means extra studying. You can actually study less if you get adequate sleep, so time spent sleeping is never wasted.