This morning, the first real evidence that the girls have started sleeping on their roosts properly. Before this, I've seen them lying, face-down, along the roost, or more comonly curled up together on the shavings. But this image from the webcam shows that they're actually roosting and tucking their heads back to sleep. (They also look a big ragged, because they're fluffing their feathers up for insulation.)
So, are you reducing the heat from the heat lamp and acclimating them to the ambient temperature now?
Yep. You start slowly, lowering the temperature about five degrees a week. When it gets cold for a spell, I'll raise the temperature a bit to help them out, but as soon as it's warm again the lamp goes back up.