If based on today's date,
for domestic flights, you can purchase the ticket up to 240 days or later. If based on the departure date, you can purchase it from a date prior to 240 days.
For international flights, you can purchase them up to 361 days or later, and purchases are available from days before 361 based on departure date.
However, the time of availability for ticket purchase may be changed depending on the circumstances of the airline.