Now have a look here...

I slept on it, and I think the second option might be much easier. Consider this again:

When casting, characters don't roll for initiative. Spells just go off at a set initiative number.That's the casting time. A fast spell might go off at initiative 9 or 10, A slower on at 2 or 3. Anyone hitting the caster before that initiative might disrupt the spell.

This way, fast spells are fast, slow ones are slow, and cripples don't have the advantage to break spells. It would also be good to have a high initiative, as you could beat the caster.

Caster's could add their normal initiative modifiers to these casting times as well.

I'd make the timing similar. In general, 1st circles would go off at 9, 2nd at 8, etc.

Players announce the spell they are casting before the initiative roll.

GMs don't have to specify, but they could announce that an opponent was casting or not.

The math is even easier, and it solves three problems: 1) Casters can't choose spells based upon knowledge of opponent's initiatives, 2) Faster characters are more likely able to disrupt casting, and 3) Casters don't need to do math every time they roll initiative. -No finger counting.

Also, strategy in casting remains: choose a fast spell if you need to get it through.

I think this is more elegant.