I live in North Texas, and I have tiny Serama cross breed bantams (Seramas are known for being sensitive to cold). Last winter, we had snow and below freezing weather and even my tiny bantams managed beautifully...we had several days when the daytime high temperature was in the upper teens and low twenties, and they acted exactly as they usually do, didn't even sit fluffed up. Chickens are actually quite cold hardy with their down coats. If you have standard size chickens, I wouldn't even think twice about whether they can manage the Florida winter you describe as long as they have shelter from rain and a place to get out of the wind. A friend of ours here in North Texas winters his chickens (even bantams) in open sided, roofed chainlink dog kennels. He puts up tarps on the sides as a windbreak. His birds thrive.