First a couple of my opinions:
1. Be wary of online MBA programs. Personally, I would not do it. Group learning and discussion is a big part of most good MBA programs. It may seem annoying to have to sit and listen to your peers babble but you honestly do walk away with some insights.
2. From my experience, evening MBA programs are filled with slackers and are watered down. That does not mean you have to be a slacker but it does mean that you may be stuck in a group full of them and there is typically a lot of group work in MBA programs.
I have an MBA and will be starting med school in August. I can only speak to the value of the MBA degree and the time it will require but I thought it might help.
If you want to be the CEO of Int'l Paper or Cisco, you need to go to Harvard for the MBA; but if you just want the knowledge, don't worry about where you go.
I attended a small school in Denver, CO called the Univ. of Denver. The basic core was two years but could have been done in less if going full time.
I did not think the program was that hard compared to my undergrad in biochem. and certainly not compared to what I expect in med school. You can slack a little and still get along very well. There are a lot of "softer" courses on management and stuff that requires reading cases and discussions followed by papers. Not hard just time consuming.
As for the value of the degree; I use it every day in some way. It gives you a good understanding of how to analyze processes and how businesses come up with those sometimes goofy regulations and and financial based policies. Not to mention, it gives you a greater understanding of how to manage people and communicate effectively.
Science and medicine are obviously my real love but the truth is medicine and science are encompassed by the world of business. The MBA will teach you how that world works and why it works the way it does. If more doctors had a business degree our healthcare system might be in better shape. You can't argue with an HMO executive if you don't speak his/her language.
In short, you could probably do it even if you had to skip a few classes and were not able to put 100% into the study. MBA programs are usually willing to work with students regarding time constraints. Regardless, I think that what you would walk away with is an extremely valuable core of knowledge for your career and personal finances. I would do it again.