every black hole in the universe has a diferent history and a diferent mass and therefore a diferent spin, some may not spin at all. I cannot prove it but i can offer some reasonable observations if you like.
as for your second question i do not believe that we always use or measure time corectly because the tests preformed with atomic clocks and airplanes that set the standard we use today were accurate enoughf for todays phisics.(anybody got a onehundred didgit calculator?)
finaly as for your questions about light passing through a medium light can pass through a glass globe fairly quickly but it may take a while to pass through a lead globe. light would pass through a hydrogen globe very easily but if the hydrogen globe were as masive as black holes seem to be it might take a very long time and a specific circumstance to pass through.