As WDWKOOK said, it occurs at check-in. Since our room was booked as a Garden Wing Deluxe room, my DH waited for me out front in the car as we knew we'd need to drive around the side to go to the Garden Wing parking lot. A lovely CM named May was waiting for me at the CR entrance (security called ahead to tell her we had arrived). She met me near the front door and didn't spill the beans other than we'd be checking in "upstairs". We arrived at the 12th Floor CL where the upgrade was revealed. I must say I was shaking a little bit. We've been lucky to get magical upgrades before, but never to this magnitude.