It kind of depends on the predators in your area, but it's always safest to assume they're always waiting for an opportunity.
For instance, my local band of raccoons will check every night/early morning, but won't actually work very hard for a chicken dinner. They've never bothered scaling the 6' chain link panels, but they'll pull a head off if it's stuck through 100% of the time. Meanwhile, my opossums will go to any length necessary to get at a chicken. We also have fox that trot right past and never make any efforts. But a few miles down the road, friends have the opposite experiences. You just never know, so you have to stay on guard.
