Woah boy. You drastically overestimate the alacrity of the U.S. federal government. Also, keep in mind that existing contracts may not permit the updated policies to be "fully" implemented, and premature "termination for convenience" is a great way to screw the American taxpayer.
It seems like the language of the XO could simply specify "six months, or the soonest time which would be allowed without penalty by the relevant contracts, but in no case longer than three years."
