WoW:CVar timingMethod

Internal timing mechanism for the game engine.

0 - Default value
1 - Low resolution timer for single core CPUs and multicore CPUs that can't sync up. Updates ~64 times a second.
2 - High resolution timer for multicore CPUs that can sync up. Theoretically updates somewhere above 1000 times a second.

When the game starts up without this variable or if timingMethod is set to 0, it checks to see if your processor cores can all work at the same speed. If it passes, it gets a 2. If it fails, it gets a 1. It's best to not edit this cvar due to the following:

If you force the game to use 1 but you have a multicore system and the cores sync up, you'll be using a lower resolution timer of around 64 times a second. The game won't run as well if you're capable of more.

If you force the game to use 2 but your multicore system do not have cores that can sync up, you will experience significant timing issues like your cooldown timers and the actual spell cooldown being way off, or spell/projectile speed issues.

Blizzard says[1]:

There were some improvements made to better support Dual-Core CPUs.

This will require adding the following CVAR to the Config.wtf file located within the WTF folder inside the World of Warcraft install folder:

set timingMethod "1"

You can also type this command in-game, but will require a restart to save the changes:

/console timingmethod 1

If this does not help try setting the value to 0.

Blizzard says[2]:

timingmethod 1 is generally for systems where the cores do not synchronize.

You might run into issues like your framerate caps at 64 instead of your vsync value.

timingmethod 2 is a higher resolution timing method and you won't hit the cap with that.