SMN in the single target scenario given, kinda works like this:

Aetherflow:
Use aetherflow right before DWT.
Use fester for aetherflow consumption. Space it out so that 1 stack is used during DWT and aetherflow can be refreshed before DWT.

DWT:
Make sure you are using tri-disaster, contagion, fester, and deathflare. The rest is mostly ruin III filler.
When a dot starts to fall off, refresh with tri-disaster, and be sure to extend it with contagion. Tri-disaster, contagion, and aetherflow are all on 1min CDs, which works out nicely.

Out of DWT:
Keep up on your dots and pet dmg CDs. Lean on ruin II as filler for the most part. Consider ruin IIIs as you near the end of the fight, during mages ballad, during DPS checks, etc.