Why not just add the light in the morning and prevent any potential problems?don't worry about it, they will be fine - fully feathered chicken does not need any other chickens to survive a night (assuming your coop is dry and draft free). We supplement light in the evening and has to turn it off abruptly (no dimmer). This most likely causes some chickens to spend the night on the floor rather on the roost, but they are fine in the morning.
I see this has been asked of you already. Have you considered adding a "night light" in the coop. Now I make my kids sleep in the dark but my chickens are happy!