Here is a
link to a Florida county website that explains everything clearly and specifically states that there are no requirements for a number of days of physical presence to qualify.
Also note the caveat that you cannot continue to claim a homestead here if your spouse claims a homestead on a home in another state that you own jointly. And according to the opinion expressed in buggyone's previous link, even the legality of claiming separate homestead exemptions for homes owned individually is up in the air right now.