Your employer was 100% wrong about Florida state law making you eligible for health insurance if you work 25 hours per week. I don't care what he said. He may have actually believed it to be the case. However:
1. THERE IS NO IN FLORIDA LAW REQUIRING AN EMPLOYER TO PROVIDE ANY HEALTH INSURANCE IN THE FIRST PLACE.
2. EMPLOYERS WHO DO OFFER HEALTH INSURANCE ARE FREE TO SET THEIR OWN REQUIREMENTS AS TO WHO IS ELIGIBLE AND WHO IS NOT as long as they do so in a manner that is non-discriminatory under Title VII and related state laws (when applicable).
The above two statements are true not only in Florida, but in every state. (There is one exception, Hawaii, to #1 - I have heard rumors that Alaska is an exception to #2 but have as yet to find any confirmation.) If your boss said otherwise, he is either mistaken or lying. Period. End of statement. No further argument.
That being said, an employee's eligibility for health insurance benefit is defined in the plan document. While an employer can make only certain classes of employee eligible for health insurance (i.e. only employees who work x number of hours per week but not those who work less; only managment employees but not clerical; only office but not shop, and so on) once those classes are established every employee in an eligible class must be offered benefits. Evidently, at least initially, in your case an employee was eligible when they worked 25 hours a week. I am going to say it again: THIS IS NOT DUE TO FLORIDA STATE LAW: IT IS DUE TO THE DEFINITIONS IN THE COMPANY INSURANCE PLAN DOCUMENT.
An employer MAY make changes to the plan document with the permission of the insurance company. If the employer has changed the document to say that NOW any employee has to work 35 weeks to be eligible, that is legal. REPEAT that is LEGAL.
However, if the plan document still says that eligibility is at 25 hours per week and the employer has decided that you, and only you, have to work 35 hours per week, that is illegal, not under Florida state law but under ERISA, which is a Federal law, and possibly under Title VII.
Do you realize that in this entire thread you have not asked a single question? Do you see how much easier it would have been if you had told us your story from the beginning and asked your question instead of making unsupported statements and waiting for us to comment?