can provide some intel on this.
Basically what you need to know is everyone within 30yards of the totem will get the buff when you drop it, generally a spell is absorbed instantly so the totem is destroyed.
However if you are dropping it next to the boss (eg melee), the bait group won't be saved by the totem unless they are within 30 yards of it the moment 10 seconds are left in the duration.
What this means is that Grounding works with pulses. It has a 15s duration so you have 3 chances per totem of soaking a spell to whoever is covered by the range.
Seeing as <5s is unpractical, your best bet is <10s.
In actual Xhul fight what you want to do is drop Grounding the moment he finishes Fel Surge and everyone's boss mod is making chat balloons on top of their heads, and at the same time use Totemic Projection to throw the totem within range of the bait group. What this will do is if you aren't terrible with your aim or the group doesn't run off to Africa because of a awkward black hole, your totem will always soak Void Surge.
Personally I always let the first go off because if we need emergency cleaning someone can just pop a CD and touch both fires.
You must however be aware that if a imp cast goes through the totem will be destroyed and you will still get Void Surge.
PS: Any shaman, regardless of spec can do this solo.