the oribital period of the ISS is 92 minutes 50 seconds. Therefore they do not experience a 24 hour day cycle as we do here on Earth. So the term "nighttime" do

the oribital period of the ISS is 92 minutes 50 seconds. Therefore they do not experience a 24 hour day cycle as we do here on Earth. So the term "nighttime" doesn't have the same meaning. However there are orbits that are more heliosynchronous than others providing more solar time. At this moment it seems that the ISS is in an pass that is more than 50% solar time as can be seen on sites such as this one: http://iss.astroviewer.net/ http://iss.astroviewer.net/.