It's a trick to enter something similar to Matrix "Bullet Time". The original Quickening mentioned above is used with Arithmeticks, which is a no no in Rendezvous. The actual Quick Time Magick actually costs 900 JP in this version though. The spell alone is already intresting and useful in the sense that, for 24 MP and 4 clockticks of time passed, you can essentially give 1 character another instant turn (Just picture CID acting 5 times for example).
Fors starters, the Quick effect can be gotten from the Reaction Ability "Critical: Quick" too (800 JP) and it's generaly useful in Rendezvous if ur characters have Reraise (Chantage, Brave Suit, Grand Armor, etc) and you can't First Strike kill your enemies (due to high evade/mana shields/weapon range).
When you have Reraise, Shirahadori is not doing much to improve the real life time it takes to clear Rendezvous missions (plus you're wasting the opportunity to dish out some damage with Soulbind, First Strike, Bonecrusher, etc). Other times, things like Soulbind actually lags ur time because the damage makes no difference (If u were to 1 shot most things) and it's not enough to break Mana Shields anyway.
Let's talk about the most time consuming Rendezvous mission: Brave Story. 10 battles with 1 particular battle with a lot of Hydras/Tiamats that lag the hell out of the game (flame, flame,flame, lighting,lightning, AAARGH...).
Since we know most Reaction Abilities are not helping us clear this mission faster, provided we can live through enemy attacks by having at least 1 character alive at all times (keeping others immortal with auto-reraise), we are not wasting much by using Magick Counter. But why do that?
Well, I think one of the fastest ways to clear this mission is either by Iaido (Chirijiraden+Kikuichimonji) or Agrias/Cid swordskills (Hallowed Bolt+Divine Ruination) to hit/kill 2~5 enemies simultaneously (Chirijiraden animation is slow but the range is better, while it's slower than Holy Sword overall it can 1 shot things that Holy Sword can't, like Mustadio and every DK in the last battle).
Since Iaido damage comes from MA and Black Wiz. have the best MA, usually one subs Iaido with Black Wiz and that's it. That means we don't have space for Time Magicks - therefore no Quick spell. Except...
The difference between B. Wiz and T. Wiz MA mod is: BW 150 - TW 130 (T. Wiz DO have the 2nd highest MA mod).
BUT! By pulling out "Bullet Time" effectively, with 2 attacking characters (1 for each player) we can actually free the Support Ability slot (otherwise Safeguard is needed) AND the head slot (Ribbon) if we really want. If you think it's too dangerous/not worth to remove Safeguard, just use Reis Duelar instead (T. Wiz + Iaido + Ribbon + Brave Suit + Tynar Rouge + best MA weapon u have, in my case it's Nirvana~+3 MA).
My Reis gets 538 HP, 227 MP and 28 MA with the safe setup, 327 MP and around 40 MA (so T. Wiz actually becomes stronger than B. Wiz) with Brass Coronet and Arcane Strength (this is actually overkill, with Defense Boost you can survive Delita/CID). If both u and ur friend choose the dangerous approach (no Safeguard), u can both use Swiftness to decrease Quick cast time to 3 CT (less interrupts to Bullet Time).
But how do u enter Bullet Time and how this allows u to drop Ribbon/Safeguard? When u and ur friend have Magick Counter and Time Magicks, when there are neg. status spreader/equip breaking enemies, start by casting Quick on the other and moving to a safe place or waiting. After 3 CT, Quick is released and his reaction is triggered, making both of u enter Bullet Time and ignoring CT/turn order altogether.
He goes forward and Iaido problematic enemies then u get ur Quick turn and repeat the process if there are any problematic enemies alive (or he can cast Quick on u if ur better positioned and u Iaido instead).
If MP is a problem, use Manafont. Even with the safe setup (227 MP), in my example Reis can recover 22 MP. Quick costs 24 and Counter Magick drains MP too, but since you will only be using Bullet Time to kill neg. status spreaders (if without Ribbon), Equipment breakers (If without Safeguard) and Hydras/Tiamats, the turns you move after those beat downs will recover your MP fully and sustain it through the mission.
The reason I asked if anyone have tried this is because there are still some ways to improve the time...I suspect that Brass Coronet plus Move+3 (instead of Manafont) is faster because better positioning = less Quicks needed for multi-kills, but then MP becomes a problem unless Hydras/Tiamats are 1 shot with certainty.
327 MP = 13 Quicks, I think it's enough provided Tiamats are going down in 1 hit (so 1 T. Wiz with Swiftness and 1 with Arcane Strength can certainly pull this off - exchanging the 2nd for B. Wiz doesn't change anything).
And the reason u don't do Bullet Time non-stop (besides MP) is because it's slower than using turns to simply walk+Iaido. If anything, the standard Ribbon+Safeguard while using this strategy only in the Hydras/Tiamats battle is already better than simply Black Wiz. + Iaido.
I will meet with my friend again sometime this week, so we'll see.