SHORTLY AFTER DAWN & NOT BEFORE. I've recently acquired 2 chickens (as rescues, over 2 yrs ago now) and I do professional animal rescue. I'm around wildlife a lot and knowing coyote activity -- and their love of chickens, dawn & dusk are their fav times to hunt. They're known to be out on moonlit nights and during the day when temps are about 60 degrees give/take 10-20 degrees. They'll wait out a bad storm when there's blowing wind too and then hunt right afterwards. I let out my chickens to roam my fenced yard only after dawn (usually right after) and only when I'm home and can monitor them. My Pit Bull rescue has also been conditioned as their protector who is also allowed the whole yard only when I'm home. --Lets hope she doesn't relapse --HA! Although NEVER an incident (yet). She actually cowers if they get upset about something. Its quite hilarious actually. AND they keep her company (through their fence) while I'm away.
My chickens don't mind the rain & a little wind. They seem to find more worms that way!
I'm currently working on an automatic chicken door that opens when they approach and closes behind them so they can come & go as they choose to lay and keeps the birds & squirrels out of the food inside. My first attempt freaked them out so I have to put a 60 sec delay in the circuit and scoot the pressure plate to the beginning of the walk before they can even see the door. That way, they'll still go in on their own just before dusk as normal --provided they can still see the light on in the coop from the base of the walk. So, I'll have to add a plexiglass window. FUN!!!

Never thought I'd love having chickens so much!