That's when you hit horn of winter for the free runic power
You should be using it sooner than that. It's free resources for a resource-constrained spec, you should be slapping it on cooldown so long as you won't cap any other resource or potentially waste any procs/buffs. It's higher priority than a few little tiddlies.
One day dude, I'm just gonna get off the bus, and I'm gonna run in the woods and never come back, and when I come back I'm gonna be the knife master! -The Rev