It does make a big difference. 24 hours within departure time your ticket become non changeable. Airport checkin won't touch any avios ticket as it's dealt by a completely different ticketing team. Only in case of cancellation they can change the ticket. So if you can see that if over 24 hours of your currently flight is there any avios availability on the other flight, if there is you can ask to change it but you need to call. There will be a change fee per person. If it is CW airport might offer a fixed amount of upgrade fee to First and can be done on a avois ticket, however there is a high chance that by that time First will be more full and they won't do it at the airport. What you don't see online for example is how CW or PE is overbooked, how many staff standby, etc.