away from fantasy, back to the OT:
Premeditation is working during dance on current PTR.
the buff refreshes every 2ish seconds and does not require "real" stealth.
oh, and you get BOTH the SnD duration AND the 2CP if SnD is running.
if you use Enveloping Shadows or have enough mobs for 5CP SS to recharge SD fast enough, you can stack SnD to over 5 minutes (i stopped at 5 min displayed)