Can my landlord change the term dates on the lease under FL residential landlord tenant laws

Yes. The written lease governs. If your lease says 12/8/08, that is what controls. The problem you face is that the landlord may claim that your notice is late or that you owe rent through the 28th even if you move on the 8th. Be sure to provide notice of your new mailing address after you move. You want to know if they sue you so that you can raise your defense and seek a hearing before the judge. Keep a copy of the lease. Do not write on the lease. Keep a separate note book to keep track of any changes regarding the lease termination.