landlord tenant laws in florida state, tenant's right to sublease apartment

You are the friend's landlord and so you can give him the appropriate notice. Is there a written lease? If not and rent is due on a monthly basis then you probably have a month to month tenancy as you mentioned in your question. You are only required to give fifteen days notice prior to the end of the monthly period. review Fla. Stat. 83.57 which i have included below:

83.57 Termination of tenancy without specific term.--A tenancy without a specific duration, as defined in s. 83.46(2) or (3), may be terminated by either party giving written notice in the manner provided in s. 83.56(4), as follows:

(1) When the tenancy is from year to year, by giving not less than 60 days' notice prior to the end of any annual period;

(2) When the tenancy is from quarter to quarter, by giving not less than 30 days' notice prior to the end of any quarterly period;

(3) When the tenancy is from month to month, by giving not less than 15 days' notice prior to the end of any monthly period; and

(4) When the tenancy is from week to week, by giving not less than 7 days' notice prior to the end of any weekly period.