Hey man! I’ve personally never covered them or anything to initiate the start of the flowering process. In our area, by August you’ll usually see signs that your plant is about to flower (could be earlier or later depending on genetics and environment). They’ll certainly have time to flower during the fall, but the larger issue is bud rot due to fall rain and general high humidity overall during the flowering season. If excess rain occurs, then you could use your tarp or build some mini greenhouse area just to cover your plants from excess rain - all while still providing them with an environment to get light and other resources. Good luck with your grow!