Some airports are not staffed all day so where you are flying from matters in this context.

Assuming the counter is open, the rules say 6 hours.

• All baggage must be checked at the airport at least 40 minutes prior to departure on domestic flights, and 60 minutes prior to departure on international flights.
• If you are traveling to an International destination, please check in at the ticket counter.
• Baggage will NOT be accepted for check in more than six hours prior to a flight's scheduled departure time.