Basically, you are like any other medical student Monday - Friday from Aug - Jun. No other military responsibilities other than wearing the uniform to class, signing-in 3x per week so they can make sure you are still alive, taking a physical fitness test (every 6-12 months) and maybe one 10 minute uniform inspection per year. Even though most classes are optional, class is over 2-3 times per week at 1120 with the rest of the time allotted for independent study (Dean's Time). At the end of your MS-I year, you spend 1 month at an active duty base seeing what the real military does (1-8 stress-free hours per day depending on what you want to do and where you go) and 5 days in the 'field' practicing military medicine while simulating a deployment (in PA). Needless to say, when you are in school, all you have to worry about is school with 'camp' activities during the summer. By the way, you get normal breaks during national holidays, 2 weeks at X-Mas, 1 week off for spring break and 1 month of leave in the summer. Take care and good luck.
Falcon95
USUHS, MS-IV