The discription of the spel says:
After the battle, you can dismiss area spell effect at will. You must be out of combat and within a 100-foot range of the spell's effect. Dismissing a spell is a standard action that does not spend spell slots and does not provoke attacks of opportunity.
Which is not true. You can use it in battle. You dont need to be out of combat.
Is there something I dont understand about "beeing in combat"? Or thats just misleading info?