I don't know honestly because it can vary so much... depending on the mechanics of the fight.

Generally though when I'm approaching single target boss mobs... you know its going to be a marathon fight... so...

I don't generally use Tri-Disaster until later in the fight when I know I'll have to be dodging mechanics.

So I'll start with a Bio 2, Miasma, Bio combo... then a Contagion.... and a Quick Cast + Shadowflare... then Rouse +Spur + Enkindle... depending on my mood.

At that point I've got 30 seconds worth of DoTs going and can Fester at will,

So its generally Fester>Ruin 3, Ruin 3> Fester> Ruin 3> Ruin 3> Fester> Dreadwyrm Trance> Ruin 3 Spam until the 2-3 second Mark (Potentially a Tri Disaster in there somewhere) > Deathflare

If its towards the end of the fight I'll kick in Raging Strikes too.