Haven't even hit 76 yet... Or I would have done it. I've only been on the game for about 12 hours total since the update, and 10 of those have been LS events. I also just spent merits prior to the update (moronic, sure), so I haven't even been able to pretend to finish the genkai.
The multiplier is nice, to be sure. It'll help us in that first few moments of getting a fight started. A 10 minute timer is ok, since most of the time, you'd want this on the big boss fights, and those don't happen more often than 10 minutes. At least, not yet. Once they do, sure, it'll be annoying as hell. I don't like 10 minute timers, either, but so far, it won't affect what we're doing.
Leviathan - PLD90, BLU90, MNK 90, DRG 78