Sales manager in Florida, is it legal that employer changes his schedule without notice and make him work 10-12 hour shifts

There is no Florida or federal law prohibiting an employer from changing a work schedule without notice and requiring an employee to work a difficult or unreasonable schedule. As long as he is not being treated differently due to some illegal reason, such as discrimination or illegal retaliation, there is probably little he can do legally. I assume that as a sales manager, he is exempt from overtime, but it would not hurt to examine the allowable exemptions under the Fair Labor Standards Act to make sure that he is actually exempt.