MKR once posted a nice bit about known incubation extremes so perhaps will again. I don't remember the exact numbers but only that it was a wider range than you might expect or is probably recommended.
As far as gender determination, it's only via chromosomes in ball pythons, not by temperature. Female ball pythons have zw sex chromosomes and males have zz. Since they are the opposite of us in that the female has the unmatched pair it's the female's genetic contribution that determines the gender of the offspring (the xy father determines the gender in humans rather than the xx mother).