with max refresh haste i guess you can get it down to 15 sec (its naturally 30 sec reuse with 60 sec duration at 50).
Not so sure on the "just one target" part. 

I know as a monk i can use mez every 15 sec with aum kor, drunken stance, and a psi.  I would assume rogues have something similar, i know they get buffs for refresh haste.

I see this post died out, but would like to clarify one thing..

Mezzes..  30 sec duration mez, with the same refresher -modification due to Aum Kor..
Ever tried pressing FD and re-mez the mobs?

Works fine for me..

/Uppercut