I would add it to my reservation now and reiterate at check-in. The CM's are usually very nice and willing to show you a map with available room locations, if you ask
Calling about about 10 days prior to my arrival, I was told by a CM at the hotel to call back within four or five days of the date. I did and they took the info then.
Be sure, though, to talk to someone actually at the hotel. Don't let the operator transfer you to Central Reservations.