I had watched the earlier 9:04 p.m. crossing of the ISS and this lasted nearly 5-minutes at almost the same elevation as the 10:39 p.m. crossing. So why was the 9:04 p.m. crossing 5-minutes long and the 10:39 p.m. crossing only 3-minutes long? The accompanying image tells the story. At 10:39 p.m. the Sun has set further, so the ISS is illuminated for less of its course across the sky. As you can see in the image – it barely makes Ursa Major before its lights out – fascinating!