Celerity

Job Ability

Reduces the casting time and the recast time of your next white magic spell by 50%.
Obtained: Scholar Level 25
Recast Time: Stratagem Charge
Duration: 1 white magic spell or 60 seconds, whichever occurs first

Celerity is a stratagem, which obeys different usage rules than typical Job Abilities.
This ability's casting time reduction does stack with the Light Arts reduction and any other casting time reductions (i.e. Fast Cast). Clarrification needed, stacks 60% fast cast or works like dual wield by reducing initial or remaining delay after fast cast.
This ability also affects the recast time of the next spell, reducing it by 50%, and does not stack with any form of haste to lower it more. However, it does not ignore the slow status effect.
When wearing Argute Loafers and under the effects of the weather that corresponds with the spells element the -cast and -recast is increased by 10% (-60% cast and recast total). Was tested and confirmed.
The word Celerity means swiftness of speed, a synonym for haste.