Are you asking for income tax reasons? As far as income tax is concerned, it doesn't really matter when you became a resident of Florida, because Florida has no state income tax for individuals. What might matter is when you stopped being a resident of your previous state. It's not necessarily the same date. Since each state has its own definition of a resident for state income tax purposes, it's possible to be a resident of more than one state at the same time. You have to check your previous state's definition of a resident for income tax purposes.
For federal income tax, it doesn't matter what state you are a resident of. (It could possibly make a difference in your federal tax if you are filing as married filing separately and your previous state was a community property state.)
In looking at definitions of a resident, you may see the term "domicile." Legally domicile is not the same as residence. You can have only one domicile at a time, but as I said above, you can be a resident of more than one state.
Why is there a question about when you became a Florida resident? When did you move out of your previous home, and when did you start living in Florida? If it's more complicated than moving from one home to another, then as tagteam said, you are going to have to give more details.
