One turn as in one user turn, or all CP for the turn.
It took me 6-7 'character' turns (can't remember exact) using Vyse to kill it, my shocktroopers were level 11 at the time. This means I finish the mission in 2 user turns. You should be able to do this in three user turns max unless your troopers are under leveled.
Also Have 2 trooper doing this ambush increase damage significantly.