According to Turtles of the US and Canada, temps between 22.5 and 30 C produce successful young of P. c. floridana, with the low end temps producing all males; eggs hatched in 62-70 days at 30 C, 66-69 days at 25 C, and 70-120 days at 22.5-25 C.

The only info given for temp of P. c. concinna is that eggs incubated at 22.5 C approached term after 161-166 days,but hatchlings had many deformities; eggs incubated at some other unspecified temperature hatched in 84-92 days.

All of this seems very similar to the relevant info for red-eared sliders, so any instructions you can find for their incubation should be applicable to the cooter eggs as well.

Good luck!