Palm Harbor Publix has a trick or treat thing going on. The kids get free cupcakes and such. And CVS, Hallmark, and other businesses open at that time usually have candy to give in the plaza.
Generally, trick or treating starts between 6-7. But I have seen them as early as 4. It really depends on the parents...understandably, many parents don't want their kids out when its dark. We don't have sidewalks in most areas, so for safety, many parents bring their kids out early.
I remember in Mass, we went out only when it did get dark. But that was a different time and place. People are far more cautious these days.
I usually take my daughter out between 5-7. We bring a flashlight in case it gets dark quickly. We generally first trick or treat at Publix and then go around the neighborhood.
I believe the Town Center is doing something as well, but I don't have the info on it.
Also many churches do trunk or treat. Best to call the church first and find out