Don't 'save' the skill for the next enemy pack, because you shouldn't be focused on the skill so much as the 15 second life-cycle of the inna allies. So what you need to do is get into the rhythm of their spawning, and always hit the active skill as soon as they spawn (make sure they're all up, sometimes you won't hit enough things to spawn all 10, things get awkward as heck when you end up with staggered spawn times on the total 10 lol).

If the set-allies have been up 13 seconds and you hit the active skill, they're going to despawn in 2 seconds and get re-cast and now you're stuck with an army of standing dudes and a long cooldown on the active skill. What's happening is the active skill timer is desyncing from their rebirth. Then I'd start to notice that my dudes aren't waves, they're just standing around, the skill comes off cooldown, I'd hit it, they splash a bit, then stand back up. So what was happening to me (and I'm guessing is happening to you) is I'd run up, spawn my splashy buddies, hit the active skill and start going to town. The allies created by the set have a 15 second life span, this life span begins when they are created. I had this problem too when I finally got my full set, while leveling I'd just spam the active ally skill on cooldown because the allies made by the skill never despawn.

Diablo 3 monk build season 25