1 day old should be 95, 1 week old 90 and then drop 5 degrees per week. That is the "guideline". However, I brought my 3 day olds and 1 week olds home and my brooder was 87 and they were fine. Even at a few weeks they were ranging between 75-80 because the temp wasn't staying stable. I've had them outside for a few hours while cleaning the brooder and it was only 70 degrees. They were fine.
It also depends on the size of the brooder. If it is "guideline" temp but small surface area, they might not hav anywhere to hide and cool down. It's best to have one spot that is warm and room for them to hide and get away from the heat if they need to.