Akershus has a two day cancellation deadline.
In past trips, I have had difficulty cancelling reservations (not talking about Akershus... just regular ADRs) the day-of the visit. However, what I noted last week is that the folks at each restaurant seem to be receptive to cancelling reservations now, such as when we decided to do an early walk-in at Yak & Yeti, when we had a later reservation there. What I'm still not sure is how to get them to cancel a (later) reservation at some other restaurant. What I do is write each confirmation number (plus restaurant, time and our name) on a slip of paper (from the notepad provided by the phone in the hotel room). In the one case that "worked", I just handed the CM checking folks in the slip and asked her to cancel the reservation. I would hope that it wouldn't matter that it wasn't for the same restaurant, but I don't know.