im not an expert at this stuff. but i raised duckies and first time to raise chicks.
i pulled the heat lamp off of them when i knew they were ready... when the primary feathers came in. and i had raised the heat lamp a couple inches every week to get them use to it.
also, they didnt hang out at the heat lamp as much.
this usually happened during the fith week.
i live in tx where it gets hot, and during the day when it was really hot i turned it off. kept it on during the night though..
until about the fifth week
i hope this helps