Xeno teams stay at work until they succeed their roll, the likelihood of which depends on their skill. Geo teams stay at work until the planet is deemed surveyed - everytime they succeed a geo roll, there's a chance that the planet be deemed surveyed. Again, the skill of the geo team improves the chance of succeeding at rolls. Also, up to a point (120 skill I think?), it can lower the chance of the planet being deemed survey complete.