I'm just going to drop this here. Someone else figure it out! Reraise on WAR/WHM. Anything over a minute is weakened. I threw capped gear Haste in on a whim to try and dissociate Future Fabulous' Haste and Fast Cast.
Code:
1:45 = Omni, 27% Haste gear
1:43 = Omni, future fab, 27% Haste in gear = 60*1.75*.99 = 1% Reduction from Fast Cast
1:58 = future fab, 0% Haste in gear = 60*1.99*.99 = 1% Haste, 1% Reduction from Fast Cast
1:57 = Ambition, 0% Haste in gear = 60*2*.98 = 2% Reduction from Fast Cast
1:42 (weakened) :44 (unweakened), Ambition, 25% Haste = 60*1.75*.98, 60*.75*.98 = 2% reduction from Fast Cast
1:39 = Merciless Matriarch, 27% Haste + Omni = 60*1.75*.95 = 5% reduction from Fast Cast
1:54 = Merciless Matriarch, 0% Haste = 60*2*.95 = 5% reduction from Fast Cast
1:52 = Merciless Matriarch, Future Fab, 0% Haste = 60*1.99*.94 = 1% Haste, 6% total reduction from Fast Cast
1:51 = Merciless Matriarch, Ambition, 0% Haste = 60*2*.93 = 8% total reduction from Fast Cast
Kirschy has, in the past, expressed a suspicion that Fast Cast is only applied to recast in whole % point increments, similar to how Killer effects affect damage. I failed to find two "odd" values above to prove it, but I can go back and test with another one some day. Point is, MM is 10% Fast Cast, Future Fab is 2% Fast Cast (or 2.5%, if that's a real thing), and Ambition is likely 5% Fast Cast.