To explain why I said no (to start the year with)...and that can easily change between now and then but here is my take on things I have seen. Some people get engaged before school since they think that added commitment will keep them together. I am of the mind that if you need a ring to keep you together then you probably aren't meant to be anyways. So if you are meant to be you wont need a ring to stay together. However, if you stay together because of a ring, then thats going to be destined to fail.
B-school is a strain on and a test of a relationship if you are living together. The honest opinion is that it can be a near death sentence if you are apart...not all relationships fail due to distance but it is extremely challenging if they dont understand what you are dealing with on a day to day basis.
However, 5 hours isnt that bad...as long as she is willing to make the trip up to visit you since you are going to be too busy to do it as often then you can easily make it work. Either get engaged right away or do it later in the fall. Doing it shortly before you head to school probably wont get her as excited haha.