Mine was about 3 1/2 hrs, but I was the only one testing (all the other candidates dropped out one-by-one in the weeks leading up to the test). I felt very much 'exposed' on the floor the whole time - it was really easy for each member of the juidging panel to see if I messed up or not.
I threw several hundred punches/hand combinations/blocks/counters, several hundred kicks, demonstrated I-don't-know-how-many self defense techniques/combinations, did the forms, answered about a hundred rapid-fire questions on Korean terminology and culture, sparred about 15 consecutive rounds (once with each black belt testing that same day for their next dan or next black belt gup level), and then did my power breaks.