Maybe you could do a trial run while you're home and see what happens. My ducks are in a predator-proof run with an enclosed area for night time. Each night I go out and they march in and I shut the door behind them. Sometimes we don't make it home before dark and they are so used to the routine, they put themselves to bed. We have left them overnight when we're out of town and just leave the door open between the run and coop, and I assume they just stick with their routine of going into the coop when it gets dark - they feel safe in there. In the winter I do keep Christmas lights on in my run until about 9 so they aren't locked in their coop in total darkness for 15 hours.