I'm about the same as Rob, I use 76 as the lowest acceptable and 80 as the highest, but I try to shoot for 78.
I've never had a clutch pip earlier than 95 days, and usually it's more like 100 to 105 or more.
One year I let a friend incubate a cluch of my couperi eggs. He incubated them at about 80-83. It often went into the low 80's.
about 50% of the clutch had kinked tails. The same female bred with the same male the year before and the year after, I uncubated the eggs at 76-80 and had ZERO kinks.
I don't say, "always, never, or my way is THE way" but...
...draw your own conclusions from that. I did.