Ruin 3 has a 1.5 cast time. All of your ruin/tri-disaster skills for both Bahamut and Phoenix are instant. All of the earth elemental spells are instant, so is mountain buster. All of the fire spells have a longer cast time, Ifrit's melee combo is instant. Garuda's Slipstream has a long cast but all your elemental spells are instant.

So effectively, we'll probably be hardcasting 3-4 spells a minute depending on swiftcast availability