I've noticed that this doesn't seem to cause any lag on singleplayer, but if the chunks with these clocks are loaded by a players client while the world is in multiplayer, the players client gets network lag.
Im building a capture the flag game and have the same problem, I worked around the bug so if it gets fixed I have to reset everything, however if it gets fixed it will help in the future.
REALITYsuccz
I've noticed that this doesn't seem to cause any lag on singleplayer, but if the chunks with these clocks are loaded by a players client while the world is in multiplayer, the players client gets network lag.