It depends on how fast you are going. I'm really not sure if some states will fine you for signalling too long if you do 151 feet or fine you for not signalling enough if you signal for 149 feet. However I do believe that the purpose of signalling is primarily to indicate to others what you intend to do before you start doing it. I would signal much earlier at 75MPH than I would at 25MPH simply because it takes more time for people to react at higher speed.
500 feet
100 feet
100 feet
in florida it is 100 feet
in Florida it is 100 feet
300 feet
100 feet.
500 feet.
Answer 100 feet
500 feet.
100 ft
100 feet minimum.