I've successfully incubated clutches at 84-86, and had no issues. It does take longer, usually closer to 70 days (75 for the clutch at 84 degrees), but there doesn't seem to be any harm to the babies. If anything, I'd say the babies came out somewhat bigger and sturdier, but this was only a handful of clutches - not a large enough sample size to be sure.

So don't worry too much, they'll hatch on their own eventually. I wouldn't start worrying until after day 70.

-Jen