My best advice (given to me last year by older and wiser med students, and now verified by own experience) is to wait to start working until at least the first semester is over. That should give you a good idea of how much time you have available, and how much stress you are experiencing.
Actually having time to work varies significantly between medical schools. What's true for your friend at one school, may not be true for you at a different school. Also, some of those schools that have classes that end at noon can be somewhat misleading -- sure, you're not in lecture, but less lecture time may translate into more time spent learning stuff outside of class -- not just reviewing material, but actually learning new material.
If you discover that you have time to work, great. But if you don't think you can, I wouldn't worry about it too much. Trust me -- I was incredibly stressed about money before I started med school -- I had been working and earning a steady income for 10 years prior to entering med school -- I couldn't imagine how I would get by without a steady paycheck. But then I realized that the money I could earn with most of the part-time jobs out there wouldn't really make any kind of dent in my debt level, I had enough money in loans to live comfortably, and I'd rather be using that time in other ways rather than working.
Anyways, take the first semester off from work -- see how things go, and then make your decision.