Extradition takes as long as it will take. Generally, however, the holding state will keep your son for as long as it is reasonable to give Ohio a chance to get its paperwork together and send a team of marshals to come get him from where he is now in Florida.
Usually, though, if a defendant has no other open cases in the state where he is being held, the wanting state would get 30 days, starting from after the signing of the extradition waiver, to extradite the defendant. That's because there's a Federal Act called the Uniform Extradition Act that says that 30 days is a reasonable amount of time for an extradition to be completed.
States are free to make their own modifications and are not bound by the Act, but because Federal Law says that 30 days is reasonable and Federal law trumps state, there isn't much one can do about a delay until after 30 days from the signing of the waiver are up. Then, if there is still no movement on the part of Ohio, your son's lawyer can petition for a writ of habeas corpus to bring him before the judge for Florida to show good cause as to why he is still being detained and, if the state couldn't show that, to release him.
Usually judges keep close watch on extradition cases since these defendants can easily fall through the cracks of the system if there is no other case they are being held for. Your son probably has a public defender assigned to him if you haven't paid for private counsel. You need to reach out and speak to him or, if he has no lawyer, you have to get a local lawyer involved so that at the earliest reasonable point possible, a lawyer would be available to do a writ as I indicated before, and to argue for his release if good cause can't be shown as to why they are still holding him.