Assuming separate tickets (PNRS, booking locators, what have you), as long as you can arrive before the last flight out, and as long as there are seats, worst case (if you call ahead of time so the ticket isn't canceled outright) is the same day change fee, not the usual change fee.

I would guess that the CO GA might treat this as a "flat tire" and just put you on the later flight without the fee, but hey, you never know.