They need to be shown how to use the plate if they've never had one before - simply put them under it and they'll decide if they want to stay or not.
I stick by a true day/night cycle because the gradual dimming of light at sunset tells them to find a heat source if they want it - but I brood outside. If you simply turned off the light on them, that doesn't give them the opportunity to get ready for sleeping, which is probably why they're making distressed sounds. Best to gradually dim the light, or use natural light (i.e. a large window) to naturally dim the room they're in.