18 hours? Seems odd - it's possible that connections aren't even possible until greater than 18 hours after arrival in some airports around the world. Though it's still more than reasonable to try and find a route somewhere, at least.
I always understood the stopover to be as you were told - one in each direction for international awards. Just no mix of stopover(s) and an open jaw, and no double open jaw. And the open jaw can't be greater than either leg as that would make it two one-way awards and cost you double, basically.