How hard is to create particles/particles systems/Visual effects of magics, spells, skills

When you say “would take”, you mean YOU would take this time (1 day, 5 hours etc…) or the effect creator took this time?

If you mean -you-: Taking this time for someone that is not so much experienced is a nice shot, so it is not so hard

If you mean the creator of effect (Cokey of example): Ok, this is a little bit hard, probably particles are the hardest part of a game/content creation (Animations, characters, blueprints, environment, sound fx, particles/effects)