You want to filter at high speed upon opening your pool. The goal is to filter as much water as possible. Slow speed is for after your water is cleared as long as the skimmers work. The filter is made to run a high speed.
I like to backwash in the morning and evening until my pool is cleared. Others here don't that much. When cleared i let it rise ~30%.
Frogs in pool, where you and i live, YES. and snakes, turtles, cottontails, mice, voles, screws. have not had any squirrels yet. Big time worms, but they may have a hard time getting in your pool. As far as keeping them out, hire a Great Blue Heron.
My geese used to try to get in so i had to keep my gate closed. Years ago during closing we had a Christmas family picture taken with the all of us in pool with the kids holding the geese. People actually thought we let them swim all summer long. The geese not the kids.