If the enemy is over 80% HP or under 20%, a alert pops up. If the target is below 80k health, a "FINISH HIM!" alert shows off - so you can safely "smite" the target for the rank3 CDR.
You can edit the 80k value to your preferred threshold.
Bonus: there are custom sound alerts in this WA. If you want to use them, download the soundfiles at the dropbox link below.
Install:
1. go to your WoW folder and locate "_retail_/Interface/"
2. create a new folder and name it "wra_c"
3. drop the two soundfiles inside the new folder
4. restart WoW
Download: https://www.dropbox.com/sh/b22o3357131xhmv/AABV1s44Gx5k5RL1d-QHcFDFa?dl=0