Mine are the same age ... and I was wondering the same thing. I am in FL. It has been in the 80s during the day and 50-60s at night. I have had mine in the coop/run for about a week and a half and have the brooder light in the coop to use at night only. It is pretty high up from the coop floor .... like 5ft up... it does still warm up the coop some and provide the red light. It seems to be helping them know to come in from the run when it gets dark.
Tonight I tried to turn off the light but they all started crying out it seemed. It's almost like a brood of toddlers afraid of the dark. I turned the light back on and they quieted down. So I don't think mine are ready.
If the 5 degrees a week thing is correct -- then it looks like 6-7wks old we can turn it off at night for good. If your temps are close to what mine are here. In FL we really should only be going down to upper 60s or 70s at night by that point. If your somewhere colder, then you may need to keep your light on at night longer.
But honestly ... I'm a newbie so I am sure someone with better experience would be more helpful.
I find that my chicks actually seem to prefer warmer than required temp at night, almost as a comfort measure. they are definitely afraid of the dark & have to be weaned off the light itself. that's not so bad, because a night light helps you look in on them during the night. if they're sleeping close together I count it good. if they're piled as close as possible under the light, I count it too cool. if they're away from the light altogether - it's too hot.
they were wide awake and active....didnt look cold fluffed out and were back n forth under the light. think they are either entertaining or irritating the rest of the flock watching them from roosts lol