If you need a timer for Rare Elites in Dragonflight, you should try out Xirev’s WeakAura.
You must first download the WeakAuras addon for the string to work. Ensure the addon is installed and enabled in the live version of the game. The default game directory will be World of Warcraft/_retail_Interface/Addons. After that, visit the following link and Copy Import String.
Log in to the game and type /wa into the chat. Click the Import button and paste the copied string and you’re done.
About the WeakAura