It all depends on where the ink is going to be... It could be a fairly relaxing or painful 4-5 hours. A lot of this also depends on if the artist has heavy hands and goes deep for the line work.
I have my full back done and a lot of it I literally fell asleep with. Places to watch out for that are painful are near the sternum, on the calves, the sides of the chest, and under the arm. Everywhere else is pretty easy to deal with. Let me know if you have any specific questions for the area the ink is going to be.
I have both upper quarter sleeves, both pectorals, my full back and my right calve done and am most likely going to get my shoulders capped off and done after my fight next week.
"A pint of sweat, saves a gallon of blood." - General George Patton