1 tick = 3 seconds

Chaos Thrust + 1 Tick (230 Potency) > TT, VP, ID, DI
Chaos Thrust + 5 ticks (350 Potency) > Everything

Plebotomise + 0 Ticks (170 Potency) > TT
Plebotomise + 1 Tick (195 Potency) > TT, ID
Plebotomise + 2 Ticks (220 Potency) > TT, VP, ID & Equal to DI
FT > Plebotomise + 6 Ticks (Maximum, 320 Potency) > TT, VP, ID, ID

In other words, don't bother with DoTs when an add is about to die.