The normal ones took me about 20-30 mintues worth of trying. The one at Niflheim took me a day to complete because the area is terrible to move in, and you have to cross multiple zones just to get to the Valkyrie position. And, the Queen Valkyrie took me about 3 days worth of trying to get past her. So, all in all, it took me an aggregagte of 4 days and a few hours.