89 degrees...
No tolerance at all for temp swings. If properly hooked up to a good thermostat the temp should hold steady.
But if your asking the max or min temp ppl incubate at, I prrsonally would range 88-90, thats it. But im sure alot of ppl have had success incubating at temps lower and higher
Http://www.BCBallPythons.com
Http://www.facebook.com/bcballpythons