You can apply Bifen IT indoors and outdoors for flies in general as long as you make sure none of the spray winds up in the lake. If contaminating the lake is a concern for you there is a product called Essentria IC3 that can be used around water without worry of hurting any aquatic life. Essentria IC3 is a broad-spectrum natural insecticide that works just as well as the synthetic insecticides but without the aquatic toxicity issue.
Bifen IT is not labeled for lice and there is no need to treat outside for lice as they do not live long off of their host. We do carry products that can be used for lice control. Please take a few moments to review our article on How to Get Rid of Head Lice for more information.
Generally, after an application of Bifen IT it should take a few hours to dry outside, typically 4-6 hours.
Bifen IT is safe to apply inside along baseboards and in cracks and crevices around the home as directed on the product label.