I'm wondering if they were there for months on end before the huge invasion at the end. Because throughout the movie, the army enlister states that the last couple of nights, strange beings were seen, in the dark shadows, the cop in the beginning says dogs and other animals were acting strange lately. And I don't think aliens can plan a huge invasion in just 3 days (which is the amount of days the movie was set). It has to be they were there making crop circles and practicing reconnaissance in preparation for the invasion. The question is I wonder how long the beings were on earth.