How often should I use Condemn/Vacuum

Can someone explain how the vacuum works exactly? Do I need to use the skill every 3 seconds to make sure Strongarm Bracers proc at all times? Or is 6 seconds enough? …or 4, 5 sec?

Tooltip states that it may take up to three secs to suck in a mob, so every 3 secs seems the right answer, but Blizzard’s descriptions tend to be incomplete at best. Can anyone (who knows) explain how the Vacuum mechanism behaves in terms of actual mechanics?

Which build are you playing?

H-Bomb and LoN Bomb.

Its just to gather mobs & trigger strong arms. Use as needed.