Our temps were in the high 80's, low 90's the week we got our chicks, too. There was no way we could follow that chart bringing temps down to the 70's by a certain week of age. It cooled off at night though so we had a heat lamp in the room they were in, but no thermometer. We regulated them by their behavior, pulling their high-sided plastic brooder further away as needed. By the end of Week 3, they were outside, with a heat lamp at night, when it was getting down to the 50's. But after a few nights we turned it off, trusting that they would keep each other warm by huddling. We had no losses. For a single chick, a Mother Hen heater probably is the best option, though.