If you do it in the morning they'll be able to go back in to roost at night as it evaporates quite quickly. Ours didn't have any adverse effects & our chickens were so much happier once the dreaded mite were gone.
Your best bet is to spray with diesel! It's easy & cheap & really works. Empty the bedding out of the house & using a spray bottle spray inside & out - you will not beieve the amount of red mite that will come swarming out of every nook & cranny. You may have to repeat this 2 or ...