Quote from Skylinerw
Depends on the type of clock you used. If you were to teleport yourself via command to perhaps 1,000 blocks in each direction away from the clock, and then teleport back, the clock should be frozen to allow you to edit the command block. Otherwise you may end up needing to use MCEdit to remove the command block.
I used the exact same clock as in the video, I did everything the exact same as in the video, the only thing I did differently was made the radius 0