Not sure this has ever been my experience. I've walked away to grab lunch, or been interrupted by a lengthy phone call and forgotten I was mid-survey, only to return several hours later and still finished the survey. Only when the delay was patently excessive (i.e. returning the next day to an open survey), do I recall getting kicked out. In fact, if I spot a potentially high-reward survey shortly before I need to leave the house, I'll go ahead and start the survey to hold my place, then pick it back up after returning home, and rarely have a problem.