If your temps are warm you can probably move them out of the brooder before they bump their heads on the light bulb. I sure wouldn’t turn it on. What are your temps outside? They are sure cute little big ones!
I guess it is possible. Its a old method that my brothers always used and i have used to raise all chickens i have ever raised with no issues. Am hoping to get a heat mat at some stage though.
Average day probably 17 Celsius, night 9.... really hard to say. One day will be 20, that night it could drop to 1, next day 3. Next day 25. So kinda hard to say.
May just have to run a extension lead out to a bigger cage in the yard for a while.