From the center area of this room, move up against the left ledge, Pivot Rightface left, then proceed to do 2 Left Jumps. If the Statue is Open, Alucard will travel far enough left to make it to the next room over, triggering a change in the music that you can use as a cue. If the Statue is closed, part of Alucard's jump will be interrupted, shortening the horizontal distance covered and Alucard will still be inside the Clock Room.