I can't remember the duration, maybe around 10 sec.
Everyone can burst their skills to a target and kill it(except cash player and defender) and
she has around 16m AoE stun and silence that pretty good enough to kill the marked target.
the role of each classes change from early to late game
Defender can't defense anything at all in early game, but late game she become unkillable with high damage.
WP is very OP in early, but reduced to initiator in late game ( still gain lots of kills from burning)
Sentinel's power will slowly fade when late game is coming for her(lack of AoE skill)
Punisher will become mega carry in late game, can get most kills in Battleground
Medic can change from support to battlemage with just Unique mecha
SW role in late game is to sneak pass enemy's front line and take down the range class... or kill the separated player that wonder around too far from the battle.
FYI; she can cast buff while stealth
Sad but true, if you want a lot of kills, I recommend WP or Punisher