Basically, a recap:
Visual/SFX
- Up to how long you want / seems logical for the unit to play its Animation you want.
- Let's say an Exploding Animation that takes 3.5 seconds.
Dummy Caster
- 2 seconds.
- Although most of my dummy caster (solely for casting spells) I put for 0.5 seconds, and it works.
If you want to become more efficient, use only 1 Dummy Caster for the entire spells (in the map).
You create a Dummy, and save it as a variable, and use the Dummy for all types of spell-casting.
This way, you're only using 1 Dummy for multiple spells, more efficient and less unit creation, leading to a good long-run gameplay.
But it also depend on the nature of your spells too, which can share, and which cannot share.