Timeline of falling into a blackhole For some "average sized" black hole, how long would it take for a distant (spacesuit-wearing!) astronaut to:


be able to see the gravitational lensing with the naked eye 
clearly feel the gravity gradient
reach a lethal gravity gradient
cross the event horizon


Ultimately I'm interested in the subjective experience of a human falling into a black hole. Would it be drawn out and unpleasant? Or is it that by the time the gradient would be painful, there'd be barely any time at all before annihilation?
Interestingly enough, Neil deGrasse Tyson, an american astrophysicist, wrote a book titled Death by black hole.

In this video he goes on to explain the details of what you asked, the subjective experience of the astronaut being sucked into the black hole. It is definitely painful!