You can still move ADRs the day-of the reservation.
We had a member of our family get suddenly sick on our trip a few weeks ago. We wouldn’t have been able to make our ADR, so I just moved it in
MDE to a date 6 months in advance, and then cancelled that ADR. We were not charged the cancellation fee.
I know we could have gone to the restaurant’s podium and explained, but that just wasn’t something we were able to do that day.