The time required to activate the SFX. The default time is actually one turn (like normal actions).
Magic spells require 1 dice turns. A spell that takes one turn or round – a normal action – costs +1 Plop.
SFX requiring additional activation time cost -1 Plops per additional turn.
Plops can be used to reduce the Activation Time, as if using the Go Faster stunt.
It would be important to know if the SFX is a task or an operation.