You would need a Very Very large secluded area, a few hundred acres at the very least to sustain something to last that long. Or a very small player cap just to keep things interesting. People get bored and "wander" aimlessly if they are not entertained enough. It would really have to be a very well disciplined group of players, not your average skirmisher etc. Just my two cents. A 48 hr OP would be fun...72 might be pushing the fun bar a bit out of my reach.