1. TO change your ticket, forget about it. You will be on line holding more than 1.5hrs then they will charge you 24-35% of your ticket cost to change the ticket, even though you paid more as FLEX ticket.
2. If you be late more than 2 hours before departure, you might loose your ticket based on availablitliy. They once sold my ticket last year to a standby passenger when I arrived 1.5 hours prior to my departure to Guadalajara from Mexicali.