How long does an overnight guest have to stay in my home before they become considered a tenant with rights under the law?

A guest staying with you will not obtain any "rights" under the Florida Landlord Tenant Act unless he or she signs a lease or a verbal lease is created. I'm not sure if you are asking because you want to evict your guest or if your landlord would have to evict the guest if he evicted you. I would need more information to fully answer your question.

Only a tenant may be evicted. Guests do not magically become tenants unless the landlord agrees and accepts rent from them. Otherwise they become occupants, whose rights rise and fall with the lease holder. That being said, it is unwise to physically remove somebody from a home without resorting to the courts. All persons should leave voluntarily if anything.

A person cannot get ownership rights in a place by simply living there. However, a former eviction still may be required to remove them.

There is no brightline unfortunately. Much of this would depend on the residential intent of the parties and proof of that. While its possible a 24 hour presence on the property could be part and parcel of a "tenancy" i.e. they just moved in, most courts would look for corroboration of such intent like, they brought all thier personal belongings, changed address, had documentation such as a lease, e-mails or such things. Regardless, for future notice, a law enforcement officer will NOT typically remove a person you allowed to be on the property voluntarily. because though there is no tenancy for an eviction, you may be forced to resort to having them removed from the property for unlawful detainer which is similar. In the future, don't invite anyone to stay with you at all that you can't trust 100%.