By the way I have done 5 years active duty and one of those years I was in Iraq.
your initial contract for for 8 years total.  You still owe them 3 years.  Now, you COULD ignore them, but at what cost?  They may or may not decide to hunt you down and drag you off kicking and screaming, but more likely what would happen is that your chances of getting any kind of loan, Federal or otherwise, just dropped down to nil.  zero.  nada.  and if you get pulled over for runninga  stopsign?  you just may find tourself in jail awating the Army's convenience to decide whether or not you are worth the trouble to court martial you.\n\nWorth it?
The instructions for the form do allow for some leeway in the "how long do you plan to stay" question.  Still, you should call the office at your school that produced your I-20 form to make sure that they didn't make an error.  As you read, the I-20 specifically asks about the "normal" term of study.  If your school feels that 36 months is normal, put that on your DS 156.  But if you call them and they say that they made an error (which seems unlikely), then you should put whatever they tell you is the correct term of study.