What is your setup like? Type of lighting, temps, humidity since u switch to flower?
Usually burning means lighting is just too close, how far is your selected light from the plant.
I don't think one heat stress problem will cause it to hermie, is it truly the first day of flower or just the first day of 12/12, big difference.
Pics always help buddy but with a little more info I'd have more for you, also what lighting was it vegged under and how long?
FJG