Temperature change question for first night outside.

Put a thermometer in with them and lower the heat source if needed.

 

They don't need heat anymore. But, since you seem very concerned, I'd suggest putting the lamp in the coop. Just don't center it. Put the heat at one end of the coop and as far from the roosts as possible. Then, when they choose cold roost sleeping over the heated floor, you won't have to stress about removing the light.

FWIW, mine chose the cold roost at 4-5 weeks. Those feathers are excellent insulation.

 

Good advice so far. Your chicks are equipped to withstand way more cold than you'd be comfortable with.

Only a little acclimatizing is necessary. Since the room they are in is cool, take away the light all together. Ignore the frantic chirping when night comes. They are only protesting the dark, not the lack of heat. If you want to quiet them, put a night light in the room for a little light. Chicks are no different than toddlers. They assume there are demons in the dark conspiring to eat them.

I advocate taking chicks outside during the day for the few days preceding moving them into the coop. This will acclimate them to outdoor temps as well as get them familiar with their new home.

You are going to find out just how much chickens abhor change. You can make life easier on yourself and them by getting creative to find ways to mitigate the changes to make the transition smoother. Bring something from the brooder with them when you move them into the coop, for example.