Gee - it's just like diplomacy. Think how many man-years are spent ironing out the details of treaties, alliances, trade agreements, etc, in the real world.
Graeme's essentially right : you can ask for a 5 turn NAP, a 10 turn NAP, etc,
or you ask for a NAP with a 3 turn, 5 turn, whatever, notification when the NAP is ending.
If you just ask for a NAP with nothing else specified, it's simply signaling intent not to attack, but either party can say "NAP time is over" at will.
