I have an Aeroplan reward booking within Canada.

On the return leg of the trip, I want to change from an afternoon flight to a flight leaving shortly after midnight, the next day (i.e. I'm on the flight leaving at 4:30PM and want to leave 8 hours later at 00:30).

I know I can pay $55 plus the difference in points to make the change, now.

But is it possible to make the change at the airport, on the day of the flight (subject to availability and a $50 change fee)? The complication being that the flight I want technically departs on a different day?

I am pretty sure there will be space on the later flight, it's OK if I don't get it. But if it's impossible to switch on the day of, maybe I'll bite the bullet and lay down some points to confirm it now.

Anyone know the rule here?