Why is the answer not B?

If a rock group performs at 10, then none of the folk groups can perform at 10, which means that Q and T must be the bands that perform at 10, because P is already slated for either 6 or 12. That means that the only open places for the folk groups to perform would be at the 8 o'clock slot and whichever slot not taken by P. Am I missing something here? Please explain.