Book 11 months out. (I am not joking)
Generally you can book 331 days in advance. If you know that far in advance, book your flight to MCO 331 days in advance have them put it on hold and when it's time for the return book the return and process the ticket.'
Now if you don't know 331 days book as SOON as you know. Be flexible, try to avoid Monday am, Friday pm. THey think they can sell those tickets to business travelers like me and don't give as many freebies.
The number of free seats is a closely held secret, but it's less then the number of folks wanting to use the free tickets.