I was an ADN RN for a little over 2 yrs before doing an online RN-BSN program, finished that by the time I had been a nurse 3 years and the immediately started my MSN-NP program. Let me tell you what to expect if you haven't had a lot of experience when you start. If you are a quick learner and "good student" (for lack of a better word), you should be okay. You will work harder than some of your more experienced classmates in certain ways because they are already familiar with more drugs, interventions, etc. I am a "good student," and have found myself having to look up more than my peers during class simply because I haven't become familiar with certain procedures or whatever. Also, I have explored a couple different areas of nursing to widen my perspective, but I wouldn't recommend starting grad school with less than 5 years nursing experience unless you honestly feel you are prepared.
Don't rush into grad school... enjoy being a nurse first... that way you will appreciate moving on when you're ready, and I think you'll know when that time is. Some people realize once they've finished undergrad that nursing is not for them, or they find themselves at a loss for finding their "niche." Allow yourself to explore what areas you do and don't like... this will make a huge difference in determining your specialization (i.e. family, acute care, pediatric, etc.).
Best of luck to you!! Let me know if you need any more info...