When my leader yells "OFF BELAY," I prepare to remove the rope from the device but answer "BELAY OFF" just before actually doing so just in case there was some communication error. If you are ready to unscrew the locking gate and remove the rope, it only takes a second after verifying that it is the right time to do so. I think this is really important if there are any other parties climbing nearby, where the chance of crossed signals exists. And of course using first names can help as well although I got taken off belay while leading once when some one else had a belayer with the same name...