I have my light on a cheap timer. Like yours OP, it's just a 40w bulb. It comes on around 8:00 and goes out around 9:00. I did this to "train" them to go inside the coop at night (and worked like a charm). Tonight was the first night they went in without the light
And yes, they will always squabble a bit when trying to get use to the dark, but they typically settle down within 10 minutes or so...
