I think she took 2-4 hours (not sure) haven't seen it in ages. But she took 5 hours and 44 minutes on soloing one of Horn Tail's head. (It's a she, said so herself on the Youtube videos).
But still, sitting on a computer for so long isn't good for you in any way. My butt gets sore and I need a break after 2.5 - 3 hours playing.