I hope this message finds you well, present circumstances excluded. I am a licensed attorney with over a decade of employment law
Benefits, such as insurance and vacation leave, are not specifically covered under statute in Florida or the federal government relative to proportion of accumulation relative to time worked.
Therefore, it is legal, in a pure sense, to do what you employer is doing UNLESS: (1) they are violating their own policy relative to what you have accumulated; or (2) they are discriminating against you based on your age, race, gender or handicap is how they give you benefits relative to other individuals.
If you have evidence of either of the aforementioned two issues, then there are legal avenues of recourse available to you.
Otherwise, this is legal.
Let me know if you have any other questions or comments.
Please rate my answer positively as well.
Best wishes going forward!