With my previous flock, the time they went to roost changed every night by about 2-3 minutes, unless it was cloudy, cold, etc. Summer solstice was the latest, at about 8:45 here in the upstate of SC. Around the winter solstice it was more like 5:45. Currently, its between 8:15 and 8:30, and its with a new flock manager running the show, and he is a little new at it.
As an aside, my coop has 2 windows on the front side that stay open from early spring through late fall, and closed mainly when the temps get pretty low. One of the funniest things I've seen is when the first cold nights arrive and those windows get closed. It changes the amount of light inside the coop, and affects how easily they can see to get up on the roost. A good rooster has it down to a science. There is always enough time to get on the roost, settle any roosting spot disputes, and calm down while there is enough light. Unfortunately, closing the windows for cold nights to early throws a rooster completely off his game. My boy Vic walked in at his usually time, clucked, poked his head out and looked up at the sky, went back in, clucked, then walked outside and stared at the sky as if to say "What the heck? Am I losing it?"
Ken