Be prepared for almost anything:
It could be in the low 80's (unusual)
Expect more in the high 60's to low 70's for daytime highs.
Overnight can get chilly. After the sun goes down (which is giving the warm days), it cools off considerably.
I always find it interesting to see all the day guests vacate the parks early because they only wore shorts and a T-shirt during the day. After sunset it will drop to 50 or lower. Remember, sunset in January is early.
Also be prepared for cold temperatures. If a cold front hits up north where it's below zero, that same front can push Florida temperatures below freezing. If you keep an eye on the weather forecasts before your trip, you'll have some idea of what to expect.