In the wild temps I am sure temps move quite a bit.

I like to stay around 88-88.5 to give it room to heat up a little if the room heats up(I live in Southern Cali). I have seen it spike up to 92 on hot day with no ill effects. Most incubators are designed to heat up but not necessarily cool down. If temps are steady during cooler months I may go to 89-89.5 still leaving room to heat up a degree or two.