Any stat buffs he casts will be increased in duration by 40%
Shout, his USB, BSB1, and BSB2 will all get increased stat duration by 40%, but the haste will NOT be boosted (it's a status, not a stat)
Chant will not be boosted at all, because critical boost and the bubble are both status effects like protect, not a statistic buff
Wall being cast by Ramza (through roaming warrior) will also be increased by 40%, as well as most stat boosting roaming warrior buffs like faith's, etc
Protect, Shell, Regen, Haste, Reflect, etc etc will not get a duration boost because those are all status effects
Short version:
Shout / BSB2 will add 35 seconds of ATK buff (with LM2) instead of 25
Shout / BSB2 will still only add 20 + mind/40 seconds of haste no matter what