Miami Dade Property Tax Assessor's office determines the assessed value of all properties. You can appeal their assessed value, but not until late August once tax notices are sent out to home owners. To appeal, you must file "A Petition for Market Review" with the Value Adjustment Board and wait for a hearing. As stated on their website... "The Property Appraiser's office conducts an "Interview Period" when additional resources are dedicated to providing taxpayers with an explanation of their assessment. Differences of opinion on value and any discrepancies should be discussed at this time."
The deadline to dispute is September, but I would encourage anyone to start right away.
I cannot tell you what the custom is in Miami. If you have an agent, they should be able to answer your question and walk you through this.