My Dawnstone Crab seems to share a cooldown with the Monarch Crab. When I pop the Monarch I end up with at least a 30 second cooldown on the Dawnstone, and from having a macro that casts one and then the other, I haven't been able to see the Dawnstone go off.
Perhaps the tortoise is different?
Edit: I was wrong! They don't share a cooldown. Awesome.

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No really, I'm not
addicted.