Rend World Buff timer is unpredictable

I don’t know how Rend World Buff works. The Nova World Buff addonds says that layers has 2 - 3 hours cooldown, but suddenly its appears the message “Rend will drop in 6 seconds”. Its hard to get Rend when this happend, someone know how to catch it?

you just have to be there when it drops

Likely a new layer appeared and someone dropped rend. Some things i have payed attention to is to watch when an ony timer is gonna go because sometimes people will drop a rend right after. Another is to look at your server discord as they have planned drops.