Originally Posted by CO Insider

Hi Bonehead, please remember that you may only switch to flights departing within 12 hours of when you're making the request (I say this because I see that you're booked well over 12 hours from now). Within 12 hours we automatically open up all main cabin classes of service for any flights that are still booked below capacity. That means a flight that's outside of the 12-hour window may not be available in your fare class now, but will be opened up at the 12-hour mark if it's indeed booked below capacity in the main cabin.