True, but because it is a variation on Xeno's Paradox it is not possible to ever actually achieve a perfect 17 minute crossing. The smaller the steps of each pair, the closer the timing will be, but it is NEVER possible to achieve the goal.
I too missed the point that they could be left standing in the dark. The flashlight caused me to reach the false assumption that they always had to be in or have some light. I even pictured the puzzle as a covered bridge with lights at each end but pitch dark inside. I must have also assumed the 4 people would not want to stand in the dark. It is funny how personal tastes and experiences can color the way we approach a problem, isn't it?
Koala, the poster formerly known as Space Turtel