The Fall River is always cold and clear and always safe for the fish. I know early morning sessions have been productive and I will also recommend beating the heat and the crowds by going from 5 PM to dusk if you have that as an option. 
Remember the hatchery access is 7am to 7pm. Mid-day fishing is good of course, it is just more crowded in the popular places. 
PMD’s, Yellow Sally’s, Olive Caddis, BWO’s Midges, Hoppers, Ant’s, Beetles, Jigs, Streamers, Zebra’s and Purdy’s. 6x and 7x will serve you well here.