well, i know the 5 degree trick, but in all honesty i have a mixed bath of 2-3 week olds, and its much lower under the heat lamp than would be suggested for even the 3 week olds, but ive ben adjusting temps based on them and not the thermometer and even now with the lamp almost off they still sleep, even at nights, scattered around the pen comfortably, every so often ill find a younger one snuggled under the wing of an older chick, but its not that frequent.
id say if there without a lamp already and doing fine and are well feathered the temps should be no problem. check on them the first few nights (especially if theres a cold snap come through) but i wouldnt worry too much.